2.875 Mechanical Assembly and Its Role in Product Development
Sears Craftsman Screwdriver
Mechanical Assembly and Its Role in Product Development
Supplied Once a day
In-house
Material
Inventory
Set-up Time: 10 min./Batch
6. Main Housing
1
Grip Housing
Assembly
6.1 Motor + PG1 Sun Gear
26
27
Transmission
Assembly
4
8.3 PG1 Ring Gear
25
8.9 Locking Gear
2
8.1 Hi/Lo Lever
29
7.2 Gear Housing
8.7 PG2 Washer 21
30
6.1. Motor Assembly
2-2. Floor Layout and Parts Flow
8.3. PG1 Internal Gear
8.1. PG1 Washer
Grease
8.6 PG2 Pinion Gears
12
5
8.2. PG1 Pinion Gears
18
Grease
F
8.9. PG2 Locking Gear
17
14
Pool
Slider
Packaging
Parts Shelf
Table
Transmission
Assembly-3
8.6. PG2 Pinion Gears
3
Once a day
by Forklift
8.13. PG2 Carrier/PG3 Sun Gear
16
8.14 PG3 Washer
Grease
8.15 PG3 Carrier
In-house Inventory
for Final Assembly
(Pallet)
8.16. PG3 Internal Gear
F
F: Fixture
S: Snap
: Downward insertion
R: Reorient
F: Remove Fixture
: Horizontal insertion
Table
Parts Shelf
7.2. Bit Holder Housing
Conveyor
Transmission
Assembly-2
8.2 PG3 Pinion Gears
15
0 sin(U 2) 0 
1
0
0 
0 cos(U 2) U 1 

0
0
1
Final Assembly
& Testing
Table
88. PG2 Coupling Gear
8.2 PG3 Pinion Gears
 cos(U 2)

0

 sin(U 2)

0

Parts Shelf
Pool
8.14 PG3 Washer
7.1 Shaft
Storage for
Trans.
Housing
Fixture Tool
8.7. PG2 Washer
8.13 PG2 Carrier
28
Parts Pallet
8.4. PG1 Carrier/PG2 Sun Gear
8.15 PG3 Ring Gear
13
Cycle Time : about 70 sec.
1 worker
8.10. Hi/Lo Lever
8.4 PG1 Carrier
11
8.8 Coupling Gear
Cycle Time: about 70 sec.
Cycle Time : about 70 sec.
1 worker for Grip Housing
1 worker
3 workers for Transmission
(Process Time:226.89--> 193 sec. by 15% tool efficiency)
6. Main Housing
RSF
8.12. Fastener for Hi/Lo Lever
19
20
6
R
8.2 PG1 Pinion Gears
22
10
Carried Once
a day
Out-house
Inventory
In-house
Inventory
Packaging
R
23
8.1 PG1 Washer 24
9
7
Final Assembly
& Testing
Parts Shelf
Table
Once a day
by Forklift
Transmission
Assembly-1
In-house Material
Inventory
(Containers on Pallet)
Table
Parts Shelf
Grip Housing
Assembly
Closer position for heavier parts
1 m2
Assembly Sequence
8.8 PG2 Coupling Gear
8.8 PG2 Coupling Gear
22
22
8.13 PG2 Carrier
8.13 PG2 Carrier
24
24
9
9
24
9
KC#4
13
12
13
12
6
Part I D number
8.8
8.9
8.7
8.4
8.2
8.1
8.3
6.1
8.10
8.12
1.95
4
3.6
30
05
04
00
05
05
1.69
30
05
04
1.69
4
3.6
30
05
00
1.69
4
1.13
33
2.51
24
4.35
3.6
1.13
4
4
03
04
04
99
03
14
03
03
03
03
99
03
14
03
99
03
13
14
80
02
39
83
2
4.5
4.5
12
2
7.5
2
2
2
2
12
2
7.5
2
12
2
5
7.5
9
5.5
3.5
6
3.95
8.5
24.3
12
3.69
11.5
16.8
3.13
6
6
12
3.69
11.5
16.8
12
3.69
9
8.63
18
8.01
7
20.7
226.89
1
1
3
1
0
1
3
0
1
1
0
0
0
0
0
0
0
0
0
1
0
0
13
8.6 PG2 Pinion Gears
8.6 PG2 Pinion Gears
8.6 PG2 Pinion Gears
12
15
11
15
11
15
11
8.13 PG2 Carrier
5
03
05
04
Fi gures f or
est i mat i on of
t heori t i cal mi n. of
part s
KC#3
8.8 PG2 Coupling Gear
4
1
1
3
1
1
1
3
1
1
1
1
1
1
3
1
1
1
1
2
1
2
2
31
O perat i on t i me i n
( sec. ) = ( 2) *( ( 4) +( 6) )
21
21
3
7.2
8.15
8.2
4
8.14
8.13
8.6
9
Tw o- di gi t manual
i nsert i on code
8.10 Hi/Lo Lever
Bit Holder Housing (Including Shaft and PG3 Carrier)
PG3 Ring Gear
PG3 Pinion Gears
Grease
PG3 Washer
PG2 Carrier/PG3 Sun Gear
PG2 Pinion Gears
Fixture/Tool (for Hi/Lo lever)
PG2 Coupling Gear
PG2 Locking Gear
Grease
PG2 Washer
PG1 Carrier/PG2 Sun Gear
PG1 Pinion Gears
Grease
PG1 Washer
PG1 Ring Gear
Motor Assembly
Reorientation
Hi/Lo Lever
Snap fit
Fastners (for Hi/Lo lever)
Total
7
Manual i nsert i on t i me
per part
21
2
Manual handl i ng t i me
per part
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
8.10 Hi/Lo Lever
8.10 Hi/Lo Lever
1
Tw o- di gi t manual
handl i ng code
No.
N umber of t i mes t he
operat i on i s carri ed
out consecut i vel y
Part N ame
Material Supply
13
KC#5
8.9 Locking Gear
8.9 Locking Gear
7.2 Bit housing
7.2 Bit housing
7.2 Bit housing
Heat
On/Off
3. Store
Energy
Electric Energy
(EE)
Grip
180
F/R/S
160
EE
140
Hand Force
(HF)
1.
Accept
Hand
HF
2.
Position
Grip
HF
4.
Switch
Power
120
Torque Limit
100
Torque Slip
80
EE
5.
Convert
EE to KE
Noise
Vibration
Heat
Torque/Speed
(,)
6.
Control
Torque/
Speed
Hi/Lo Speed
8.
Prevent
Reverse
Direction

Bit
Vibration
9.
Transmit
Torque

7.
Permit
Slippage
Noise
Vibration
Heat

Screw
Bit

60
Noise
Vibration
Heat
40
20
0
-2 . 0 4
-2 . 0 3
-2 . 0 2
-2 . 0 1
-2
-1 . 9 9
-1 . 9 8
-1 . 9 7
Tight/loose screw
Worn bit
Damaged screw
10.
Act on
Object
Noise
Vibration
Heat
Team Members:
Agus Sudjianto
Jared Clark
Milind Oak
Eiichi Tanabe
Gaurav Shukla
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 1 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
PROBLEM STATEMENT .......................................................................................................................... 4
3.6-VOLT SEARS/CRAFTSMAN CORDLESS SCREWDRIVER...................................................... 4
1. REPORT #1: PRODUCT DESCRIPTION ............................................................................................ 5
1.1 PRODUCT ASSEMBLY DRAWING ......................................................................................................... 6
1.2 TRANSMISSION ASSEMBLY .................................................................................................................. 7
1.3 EXPLODED VIEW OF TRANSMISSION ASSEMBLY ............................................................................... 8
1.4 CLEARANCE SPECIFICATION .............................................................................................................. 9
1.5 SCREWDRIVER COMPONENT BREAKDOWN ..................................................................................... 11
1.6 BILL OF MATERIALS .......................................................................................................................... 12
1.7 ASSEMBLY TREE ................................................................................................................................ 14
1.8 FUNCTIONAL FLOW MODEL ............................................................................................................. 15
1.9 SYSTEM HIERARCHY BREAKDOWN ................................................................................................... 16
1.9.1 Battery Module System Breakdown ........................................................................................... 16
1.9.2 Driver Mechanism System Breakdown ...................................................................................... 17
1.10 LIAISON DIAGRAMS OF PART MATING ........................................................................................... 18
1.10.1 Product Main Assembly ........................................................................................................... 18
1.10.2 Battery and Housing Assembly ................................................................................................ 18
1.10.3 Torque Limiter ......................................................................................................................... 18
1.10.4 Transmission ............................................................................................................................ 19
1.10.5 Motor Assembly ....................................................................................................................... 19
2. REPORT #2: DATUM FLOW CHAIN ................................................................................................ 20
2.1 OVERALL TRANSMISSION KEY CHARACTERISTICS .......................................................................... 20
2.2 FEATURE, MATE, AND CONTACT TABLE .......................................................................................... 24
2.3 COMPLETE BILL OF MATERIALS ...................................................................................................... 25
2.4. EXPLODED VIEW .............................................................................................................................. 27
3. REPORT #3: ASSEMBLY SEQUENCE.............................................................................................. 28
3.1 REVISED LIAISON DIAGRAM ............................................................................................................. 28
3.2 REVISED DATUM FLOW CHAIN ........................................................................................................ 28
3.3 ALL POSSIBLE ASSEMBLY SEQUENCE .............................................................................................. 29
3.4 THE MOST CONVENIENCEE ASSEMBLY SEQUENCE ........................................................................ 30
3.5 REQUIRED GROSS AND FINE MOTIONS ........................................................................................... 31
3.6 FUTURES, CHAMFERS AND LEAD INS .............................................................................................. 31
3.7 DIFFICULTIES & IDEAS IN ASSEMBLY .............................................................................................. 33
3.8 FEATURE PARTS AND ASSOCIATED ASSEMBLY TOOL AND FIXTURES ............................................ 34
3.9. FIXTURES AND TOOLS FOR ASSEMBLY ........................................................................................... 36
3.10 GEAR SET ARCHITECTURE REDESIGN ........................................................................................... 37
3.11 IMPROVEMENT HIGHLIGHT ............................................................................................................ 38
4. REPORT #4: ASSEMBLY FLOOR LAYOUT ANALYSIS .............................................................. 39
4.1. ASSEMBLY SEQUENCE ..................................................................................................................... 39
4.2 ASSEMBLY PROCESS TIME ................................................................................................................ 41
4.3 ASSEMBLY LINE DESIGN AND ASSUMPTIONS .................................................................................. 43
4.3.1 Design Parameters..................................................................................................................... 44
4.3.2 Supplied Material ...................................................................................................................... 44
4.4 ASSEMBLY OPERATION STYLE .......................................................................................................... 45
4.4.1 Assembly Line Design ................................................................................................................ 45
5. REPORT #5: WORKSTATION DESIGN ........................................................................................... 49
5.1 REQUIRED CYCLE TIME TO COMPLETE THE PLANNED OPERATIONS ............................................. 49
5.1.1 Assembly Flow Diagram ............................................................................................................ 49
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 2 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
5.1.2 Final Assembly ........................................................................................................................... 50
5.1.3 Testing and Packaging ............................................................................................................... 50
5.1.4 Transmission Assembly .............................................................................................................. 51
5.1.5 Grip Housing/Battery Assembly ................................................................................................. 51
5.2 STATION LAY OUT: IN AND OUT FLOWS OF ASSEMBLIES AND PARTS ............................................. 53
5.3 REQUIRED MOTIONS OF EQUIPMENT AND PEOPLE ........................................................................ 54
5.4 NECESSARY INSPECTIONS OR TESTS ................................................................................................ 55
5.5 GANTT CHART OF REQUIRED TIME OF ACTIVITIES AND A COMPLETE CYCLE ............................... 57
5.6 COST ESTIMATION OF WORKSTATIONS ............................................................................................ 61
5.7 ESTIMATION OF THE COST OF PERFORMING ONE ASSEMBLY CYCLE ............................................ 62
6. REPORT #6: ECONOMIC ANALYSIS AND ASSEMBLY LINE SIMULATION ........................ 63
6.1 ECONOMIC ANALYSIS OF THIS ASSEMBLY LAYOUT ......................................................................... 63
6.1.1 Estimated Manufacturing Cost .................................................................................................. 64
6.1.2 Inventory Cost and Distribution Cost ........................................................................................ 65
6.1.3 Development Cost ...................................................................................................................... 65
6.1.4 Unit Part Costs .......................................................................................................................... 66
6.1.5 Economic Analysis ..................................................................................................................... 67
6.2 DISCRETE EVENT SIMULATION OF ASSEMBLY LINE ........................................................................ 68
6.2.1 Discrete Event Simulation: Configuration Study ....................................................................... 68
6.2.2 Selection of Final Assembly Process.......................................................................................... 76
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 3 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Problem Statement
3.6-Volt Sears/Craftsman Cordless Screwdriver
September 29, 1999
Clients: Dr. Dan Whitney
Project Team:
Name
Agus Sudjianto
Jared Clark
Milind Oak
Gaurav Shukla
Eiichi Tanabe
E-mail
asudjian@ford.com
jclark15@ford.com
moak@ford.com
Gaurav@mit.edu
eitanab@ibm.net
The team decided to analyze Sears/Craftsman 3.6-Volt Cordless Screwdriver. The
product has dual-position handle design: in-grip position to work in confined areas which
can be easily converted into pistol-grip for normal screw-driving tasks.
The followings are some notable features of the product:
 Two-speed, 130 and 400 RPM, with 2-speed gear box to match the need for
applications of high speed fast screw-driving and low-speed high-torque heavy
duty screw-driving.
 Planetary spur gears to provide the torque and power needed.
 Adjustable torque clutch to match driving torque task
 Trigger switch for reverse-off-forward control.
 Impact resistant glass-filled nylon housing.
 ¼-in. hex collet with automatic spindle lock.
 3.6-volt 3-cell rechargeable batteries.
 Power supply to recharge the batteries.
NOTE:
 The battery charger sub-system is excluded from this study.
 Sum of the sub-assembly such as motor may be treated as a module.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 4 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1. Report #1: Product Description
In this report Sears/Craftsman 3.6-Volt Cordless Screwdriver is described as follows,






Product Drawings
 Product Assembly Drawing
 Transmission Assembly
 Exploded View of Transmission Assembly
 Clearance Specification
 Screwdriver Component Breakdown
Bill Of Material (Including Parts List, Function and Material)
Assembly Tree
Functional Flow Model
Functional System Breakdown
 System Hierarchy Breakdown
 Battery Module System Breakdown
 Driver Mechanism System Breakdown
Liaison Diagrams of Part Mating
 Product Main Assembly
 Battery and Housing Assembly
 Torque Limiter
 Transmission
 Motor Assembly
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 5 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.1 Product Assembly Drawing
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 6 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.2 Transmission Assembly
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 7 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.3 Exploded View of Transmission Assembly
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 8 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.4 Clearance Specification
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 9 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 10 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.5 Screwdriver Component Breakdown
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 11 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.6 Bill Of Materials
No Syst System
#
Name
1 1 Battery
Charger
2 2 Battery
Closure
3
Part
Part Name
#
1.1 Battery Charger
2.1
2.2
4
2.3
5
2.4
6
2.5
7
3
Power
Storage
3.1
8
3.2
9
10
3.3
3.4
11
12
13
14
3.5
3.6
3.7
3.8
15
N/A
Charger Contact
Plates
Battery Left
Housing
Bettery Right
Housing
Battery Cover
2
Contact Power
SUS304
1
Enclose Battery
Provide contact of battery
charger to battery
Also function as hand grip
1
Enclose Battery
Also function as hand grip
1
Enclose Battery
Baterry Housing
Fasteners
Rechargable
Batteries
Battery Cables
2
3
Hold battery
housing
Store power
2
Transmit power
Battery Connectors
Switch to Motor
Cables
Crim Connectors
Shrink wrap
Tape
Cable connectors
2
2
Connect cable
Transmit power
2
1
1
2
Hold cable
Hold batteries
Hold cable
Connect cables to battery
1
Accept hand
17
4.3
18
4.4
19
4.5
Ball Bearings
6
20
4.6
1
21
4.7
22
4.8
23
4.9
Bearing holder
plate
Torque Limiter
Springs
Torque Limiter
Base Support
Torque Limiter
Fasteners
Drive Left Housing
1
1
4
Glass-filled
nylon
Glass-filled
nylon
Glass-filled
nylon
N/A
Total of 3.6V battery
N/A
Provide connection from battery
to switch (+/-)
Connecting cables to battery
Provide connection from switch
to
Holding cable to motor
N/A
SUS304
Polypropylene
SUS304
Polypropylene
cellophane
SUS304
Accept hand control to push
Polypropylene
needle bearing for torque limiter
Accept outer cap
PS
(Polystyrene)
Hold inner and outer caps
SUS304
Push PG1
To adjust torque limiter
internal gear
Allow internal gear PG1 slippage
N/A
SUS304
1
Hold ball
bearings
Hold bearing
holder plate
Support springs
2
Hold base support to motor
N/A
1
Glass-filled
nylon
4
N/A
4 springs to privide uniform flex SUS304
suport
Nylon
25
5.2
Drive Right
Housing
1
26
5.3
1
27
5.4
1
Support grip locking switch
SUS304
28
5.5
2
Hold housing
N/A
29
5.6
2
hold drive
N/A
30
5.7
2
hold housing
N/A
6.1
Grip Locking
Switch
Grip Locking
Spring
Drive Housing
Long Fasteners
Drive Housing
Medium Fasteners
Drive Housing
Short Fasteners
DC Motor
Provide
Also to isolate noise
enclosure to
drive
Provide
Also to isolate noise
enclosure to
drive
Hold grip position
1
Convert EE to Kinetic Energy
N/A
6.2
On/Off Button
1
Connect electric
power
Polypropylene
31
32
6
Power
generator
5.1
Material
6V DC Power supply
4.2
Drive
Closure
4.1
Note
Charge Battery
16
5
Torque
Limiter
Function
1
Torque Limiter
Outer Cap
Torque Limiter
Inner Cap
Torque Limiter Cap
Clip
Needle Bearings
24
4
Quantity
Glass-filled
nylon
Polypropylene
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 12 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
33
6.3
No Syst
#
34
System
Name
35
36
37
Part
Part Name
#
6.4 F/R/S Lever
6.5
7
Bit Holder
7.1
7.2
38
7.3
39
7.4
40
41
On/Off Spring
1
Support On/Off
Button
Quantity
Function
Polypropylene
F/R/S Switch
Circuit
Collet
Bit Holder Housing
1
Control polarity connection to battery
1
1
Transmit torque Also to hold bit
Provide housing to drive mechanism
Direction Stopper
Clips
Direction Stoppper
Supports
Screwdriver bit
Planetary Gear 1
(PG1) Washer
PG1/PG3 Pinion
Gears
PG1 Internal Gears
2
Hold PG3 carrier To allow counter rotation
PS
(Polystyrene)
SUM
PS
(Polystyrene)
SUS304
4
Hold stopper
clips
Act on screw
Enclose pinion
gears
Increase torque
PG1 Carrier/PG2
Sun Gear
PG1 Sun Gear
PG2 Pinion Gears
PG2 Washer
1
PG2 Coupling
Gear
PG2 Locking Gear
1
43
8.3
44
8.4
45
46
47
8.5
8.6
8.7
48
8.8
49
8.9
50
51
8.10 Hi/Lo Lever
8.11 Hi/Lo Button
1
1
52
53
8.12 Hi/Lo Fasteners
8.13 PG2 Carrier/PG3
Sun Gear
8.14 PG3 Washer
2
1
8.15 PG3 Internal
Gear/Direction
Openner
8.16 PG3 Carrier
1
55
56
Material
Provide control for rotation direction
42
54
Note
1
7.5
Transmissi 8.1
on
8.2
8
SUS304
1
1
6
1
1
3
1
1
1
1
PS
(Polystyrene)
SUM
SUS304
SMF
Coordinate
Allows all pinion gears to rotate SMF
pinion gears
along its internal gear
Hold pinion gears Also transmit torque
SUM
Transmit torque
Reduce speed
Enclose pinion
gears
Hold pinion gears
SMF
SMF
SUS304
Hold PG2
system
Transmit control By shifting coupling gear
Accept Hi/Lo
control
Hold Hi/Lo lever
Hold pinion gears
Enclose pinion
gears
Coordinate
pinion gears
Hold pinion gears
PS
(Polystyrene)
PS
(Polystyrene)
SUS304
Polypropylene
N?
SUM
SUS304
Allows all pinion gears to rotate SMF
along its internal gear
SUM
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 13 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.7 Assembly Tree
3.6 V Dual Grip Craftmans Cordless Screwdriver
Battery Charger Module
Driver Module
Power Storage Module
Left Housing Fasteners
Left Housing Assembly
Label
Housing
Battery Cover
Batt.
Housing Fasteners
Batt. Left Housing
Housing
Charger Contact
Driver Assembly
RH Fasteners
F/R/S Lever
Hi/Lo Button
On/Off Switch
Button
Spring
Grip Locking
Switch
Spring
Transmission
Assembly
Torque Adj. Assy.
Outer Cap As.
Out cap
Clip
Inner Cap
PG1 Int. Gear Assy
Internal Gear
Washer
PG1 pinions
PG1 carrier
PG2 washer
PG2 pinions
PG2 locking gear
Hi/Lo Fasteners
Hi/Lo Lever
PG2 Coupling Gear
PG2 Carrier
PG3 Washer
PG3 pinions
PG3 internal gear
Dir. Stop Support
Dir Stop Clip
Motor
Assembly
Batt. Right Housing
Housing
Charger contact
Battery Assembly
RH Assembly
Label
Housing
Tape
Switch Module
Motor cables
Batt. Cables
Connectors
Cables
Ball Bearing
Bearing Holder
Plate
Bearing Washer
Battery
Torque Limiter
Springs
Torque Limiter
Base Support
Torque Limiter
Fasteners
Connectors
Shrink Wrap
Batteries
Crim connectors
Motor Assembly
Sun Gear
Motor
Bit Holder Assy.
Collet
Housing
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 14 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.8 Functional Flow Model
Hand Force
Electricity
Screw
Bit
Control signal
Tight/loose screw
Noise
Vibration
Heat
Worn bit
Damaged screw
Torque slip signal
Turn
Screw
Energy
Material
Information
Heat
Grip
On/Off
3. Store
Energy
Electric Energy
(EE)
F/R/S
EE
Hand Force
(HF)
1.
Accept
Hand
EE
5.
Convert
EE to KE
Noise
Vibration
Heat
HF
2.
Position
Grip
Torque/Speed
(,)
HF
6.
Control
Torque/
Speed
Hi/Lo Speed
8.
Prevent
Reverse
Direction

Bit
Vibration
9.
Transmit
Torque
4.
Switch
Power

Torque Limit
Torque Slip
7.
Permit
Slippage

Noise
Vibration
Heat
Noise
Vibration
Heat

Screw
Bit
Tight/loose screw
Worn bit
Damaged screw
10.
Act on
Object
Noise
Vibration
Heat
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 15 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.9 System Hierarchy Breakdown
Cordless Screwdriver
Battery Module
Drive Mechanism
1.9.1 Battery Module System Breakdown
Battery Module
2. Closure
3. Power Storage
2.1. 2 Contact Plates
3.1. 3 Rechargables
2.2. Left
3.2. 2 Batt. Cables
2.3. Right
3.3. 2 Connectors
2.4. Cover
3.4. 2 Motor Cables
2.5. 2 Fasteners
3.5. 2 Crim Connectors
3.6. Shrink Wrap
3.7. Tape
3.8. Cable Connectors
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 16 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.9.2 Driver Mechanism System Breakdown
Drive Mechanism
8. Transmission
4. Torque Limiter
5. Drive Closure
Planetary Gear (PG) 1
5.1. Left Housing
5.2. Right Housing
4.1. Outer Cap
8.1. Washer 1
4.2. Inner Cap
8.2. 3 Pinion Gears
4.3. Clip
8.3. Internal Gear
4.4. 4 Needle Bearing Pins
8.4. Carrier + Sun Gear for PG 2
4.5. 6 Ball Bearings
8.5. Sun Gear
4.6. Bearing Holder Plate
5.3. Grip Locking
5.4. Spring
5.5.-5.7. 6 Fasteners (3 Types)
6. Power Generator
6.1. DC Motor
4.7. 4 Springs
Power Control
4.8. Base Support
On/Off Switch
4.9. 2 Fasteners
Planetary Gear (PG) 2
8.6. 3 Pinion Gears
Planetary Gear (PG) 3
8.2. 3 Pinion Gears
8.7. Washer
8.14. Washer
Hi/Lo Speed Control
8.15. Internal Gear + Direction Openner
8.16. Carrier
8.8. Coupling Gear
8.9. Locking Gear
6.2. Button
6.3. Spring
Direction (F/R/S)
6.4. Lever
6.5. Switch Circuit
7. Bit Holder
8.10. Lever
7.1. Collet
8.11. Interface Button
7.2. Housing
8.12. 2 Fasteners
Direction Stopper
8.13. Carrier and Sun Gear for PG 3
7.3. 2 Clips
7.4. 4 Supports
Screwdriver Bit
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 17 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.10 Liaison Diagrams of Part Mating
1.10.1 Product Main Assembly
1.10.2 Battery and Housing Assembly
1.10.3 Torque Limiter
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 18 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
1.10.4 Transmission
1.10.5 Motor Assembly
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 19 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
2. Report #2: DATUM FLOW CHAIN
Transmission/Motor sub-assembly is selected for a detailed Datum Flow Chain (DFC)
analysis. The exploded view of this module is shown in Figure 7. Figure 1 shows the
DFC of overall sub-assembly. Detailed analysis of Hi/Lo speed conversion is presented
in Figures 2-6.
Datum Flow Chain for Transmission
4& 6: Torque Limiter & Power Generator
8.3: PG1 Internal Gears
KC#1
20
18
17 26
19
KC#2
8.1: Planetary Gear 1 Washer
8.10:Hi/Lo Lever
25
21
24
8.2: PG3 Pinion Gears
16
8.4: PG1 Carrier/PG2 Sun Gear
14
8.8: PG2 Coupling Gear
13
8.9:PG2 Locking Gear
12
15
Alternative
8.7: PG2 Washer
8.6: PG2 Pinion Gears
23
22
9
Alternative
8.13:PG2 Carrier/PG3 Sun Gear
11
10
8.14:PG3 Washer
8.15:PG3 Internal Gear
7.2: Bit Holder Housing
4
7
6
2
8
5
8.2: PG3 Pinion Gears
3
1
8.16 & 7.1:PG3 Carrier & Bit Holder
Figure 1. Datum Flow Chain (DFC) of Transmission/Motor Module
2.1 Overall Transmission Key Characteristics
KC#1: In order for screwdriver to function properly, Bit Holder rotation axis must be
concentric with Power Generator axis. Thus concentricity is a key characteristic.
KC#2: The distance between PG3 Internal Gear & PG1 Internal Gear is important
because this subassembly has to fit within the space provided by Transmission/Bit Holder
housing. So Stack-up length is a key characteristic.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 20 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
KC#3-#5: Hi/Low Speed Configuration and Their Key Characteristics
The gear configurations for the high/low speeds and the transition are shown in the
following figure.
High Speed
Speed Transition
8.9
8.9
8.9
8.8
8.8
8.8
8.6
8.6
8.6
8.13
Low Speed
7.2
8.13
7.2
8.13
7.2
Figure 2. Hi/Lo speed gear configurations.
There are distinct key characteristics for each configuration as follows.
 High Speed: The Coupling Gear must successfully engage to lock PG2 Carrier and
PG2 Pinion Gears together so that they become an integral unit. Therefore, the
engagement of PG2 Carrier and Pinion Gears is the KC (KC#3).
8.10 Hi/Lo Lever
21
KC#3
8.8 PG2 Coupling Gear
22
8.13 PG2 Carrier
15
11
24
9
8.6 PG2 Pinion Gears
12
13
7.2 Bit housing
Figure 3. DFC for High Speed condition
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 21 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development

Transition: The Coupling Gear must not engage with either PG2 Carrier or Locking
Gear. Therefore, the KC is the gap between PG2 Carrier and Locking Gear (KC#4).
8.10 Hi/Lo Lever
21
8.8 PG2 Coupling Gear
8.13 PG2 Carrier
15
11
24
9
KC#4
8.6 PG2 Pinion Gears
12
13
8.9 Locking Gear
7.2 Bit housing
Figure 4. DFC for transition condition

Low Speed: The Coupling Gear and the Locking Gear must be properly engaged to
become an integral unit so that the Pinion Gear can rotate around the
Coupling/Locking Gear unit. The situation of the KC is shown in the following
figure.
h
8.9
8.8
g2
g1
8.6
8.13
7.2
Figure 5. Low speed condition
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 22 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
If (g1 – g2) < 2h then stress built up is occurring (over-constrained) and the
mechanism will fail. On the other hand, if (g1 – g2) > 2h + , where  is the
acceptable clearance, then wobbling problem is occurring. The former problem is
more severe than the later problem. Therefore, the KC (KC#5) is defined by the
Pinion Gears and the Locking Gear. The success of engagement between the Locking
and Coupling gear is a key condition to this mechanism. The Datum Flow Chains for
the above conditions are shown in the following figures.
8.10 Hi/Lo Lever
21
8.8 PG2 Coupling Gear
22
8.13 PG2 Carrier
15
11
24
9
8.6 PG2 Pinion Gears
12
13
KC#5
8.9 Locking Gear
7.2 Bit housing
Figure 6. DFC for low speed condition
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 23 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
2.2 Feature, Mate, and Contact
Table
Feature
Number
Part No.
1
7.2
Bit Holder Housing
7.2
Bit Holder Housing
2
3
Part A
8.16 & 7.1 Carrier & Bit Holder
Part No.
Part B
DOF
MATE/
CONTACT
Comments
8.16 & Carrier & Bit
7.1 Holder
8.15 Internal Gear
Five
Mate
Peg & Hole
Five
Mate
Peg & Hole
8.2 Pinion Gears
Five
Mate
3 Peg & Holes for 3 pinions
Mate
Overconstrained Dofs, Clearance
Mate
Overlap of 2 plates, OverCons. With #7
Four
Mate
Overconstrained Dofs, Clearance
4
8.2
Pinion Gears
8.13 PG2 Carrier/PG3 Five
Sun Gear
8.14 Washer
Three
5
8.2
Pinion Gears
6
8.15
Internal Gear
7
8.15
Internal Gear
8.14 Washer
Three
Mate
Overlap of 2 plates, OverCons. With #5
8
8.14
Washer
Three
Mate
Overlap of two Plates
9
8.13
Five
Mate
3 Peg & Holes for 3 pinions
10
7.2
PG2 Carrier/PG3 Sun
Gear
Bit Holder Housing
Five
Mate
Peg & Hole
11
7.2
Bit Holder Housing
8.13 PG2 Carrier/PG3
Sun Gear
8.6 PG2 Pinion
Gears
8.9 PG2 Locking
Gear
8.1 Hi/Lo Lever
Five
Mate
Peg & Hole
12
8.6
PG2 Pinion Gears
8.7 PG2 Washer
Three
Mate
Overlap of 2 plates, OverCons. With #14
13
8.6
PG2 Pinion Gears
Mate
Overconstrained Dofs, Clearance
14
8.7
PG2 Washer
8.4 PG1 Carrier/PG2 Five
Sun Gear
8.4 PG1 Carrier/PG2 Three
Sun Gear
Mate
Overlap of 2 plates, OverCons. With #12
15
8.6
PG2 Pinion Gears
Five
Mate
Overconstrained Dofs, Clearance
16
8.4
Five
Mate
3 Peg & Holes for 3 pinions
17
8.2
PG1 Carrier/PG2 Sun
Gear
PG3 Pinion Gears
Three
Mate
Overlap of 2 plates
18
8.2
PG3 Pinion Gears
Five
Mate
Gear mate
19
8.1
Three
Mate
Overlap of 2 plates
20
8.3
Pinion Gears 1
Washer
PG1 Internal Gear
Three
Mate
Overlap of 2 plates
21
8.1
Hi/Lo Lever
One
Mate
22
8.13
Five
Mate
Gear mate
23
8.9
PG2 Carrier/PG3 Sun
Gear
PG2 Locking Gear
Six
Mate
Properly constrained
24
7.2
Bit Holder Housing
Three
Mate
Oversize hole
25
7.2
Bit Holder Housing
Three
Mate
Oversize hole
26
7.2
Bit Holder Housing
Six
Mate
Properly constrained
27
8.2
PG3 Pinion Gears
Five
Mate
Gear mate
8.2 Pinion Gears
8.8 PG2 Coupling
Gear
8.2 PG3 Pinion
Gears
8.1 Pinion Gears 1
Washer
4 & 6 Torque Limiter &
Power Generator
8.3 PG1 Internal
Gear
4 & 6 Torque Limiter &
Power Generator
8.8 PG2 Coupling
Gear
8.8 PG2 Coupling
Gear
8.8 PG2 Coupling
Gear
8.8 PG2 Coupling
Gear
8.3 PG1 Internal
Gear
4 & 6 Torque Limiter &
Power Generator
8.3 PG1 Internal
Gear
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 24 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
2.3 Complete Bill Of Materials
No Syst System
#
Name
1 1 Battery
Charger
2 2 Battery
Closure
3
Part
Part Name
#
1.1 Battery Charger
2.1
2.2
4
2.3
5
2.4
6
2.5
7
3
Power
Storage
3.1
8
3.2
9
10
3.3
3.4
11
12
13
14
3.5
3.6
3.7
3.8
15
N/A
Charger Contact
Plates
Battery Left
Housing
Bettery Right
Housing
Battery Cover
2
Contact Power
SUS304
1
Enclose Battery
Provide contact of battery
charger to battery
Also function as hand grip
1
Enclose Battery
Also function as hand grip
1
Enclose Battery
Baterry Housing
Fasteners
Rechargable
Batteries
Battery Cables
2
3
Hold battery
housing
Store power
2
Transmit power
Battery Connectors
Switch to Motor
Cables
Crim Connectors
Shrink wrap
Tape
Cable connectors
2
2
Connect cable
Transmit power
2
1
1
2
Hold cable
Hold batteries
Hold cable
Connect cables to battery
1
Accept hand
17
4.3
18
4.4
19
4.5
Ball Bearings
6
20
4.6
1
21
4.7
22
4.8
23
4.9
Bearing holder
plate
Torque Limiter
Springs
Torque Limiter
Base Support
Torque Limiter
Fasteners
Drive Left Housing
1
1
4
Glass-filled
nylon
Glass-filled
nylon
Glass-filled
nylon
N/A
Total of 3.6V battery
N/A
Provide connection from battery
to switch (+/-)
Connecting cables to battery
Provide connection from switch
to
Holding cable to motor
N/A
SUS304
Polypropylene
SUS304
Polypropylene
cellophane
SUS304
Accept hand control to push
Polypropylene
needle bearing for torque limiter
Accept outer cap
PS
(Polystyrene)
Hold inner and outer caps
SUS304
Push PG1
To adjust torque limiter
internal gear
Allow internal gear PG1 slippage
N/A
SUS304
1
Hold ball
bearings
Hold bearing
holder plate
Support springs
2
Hold base support to motor
N/A
1
Glass-filled
nylon
4
N/A
4 springs to privide uniform flex SUS304
suport
Nylon
25
5.2
Drive Right
Housing
1
26
5.3
1
27
5.4
1
Support grip locking switch
SUS304
28
5.5
2
Hold housing
N/A
29
5.6
2
hold drive
N/A
30
5.7
2
hold housing
N/A
6.1
Grip Locking
Switch
Grip Locking
Spring
Drive Housing
Long Fasteners
Drive Housing
Medium Fasteners
Drive Housing
Short Fasteners
DC Motor
Provide
Also to isolate noise
enclosure to
drive
Provide
Also to isolate noise
enclosure to
drive
Hold grip position
1
Convert EE to Kinetic Energy
N/A
6.2
On/Off Button
1
Connect electric
power
Polypropylene
31
32
6
Power
generator
5.1
Material
6V DC Power supply
4.2
Drive
Closure
4.1
Note
Charge Battery
16
5
Torque
Limiter
Function
1
Torque Limiter
Outer Cap
Torque Limiter
Inner Cap
Torque Limiter Cap
Clip
Needle Bearings
24
4
Quantity
Glass-filled
nylon
Polypropylene
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 25 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
33
6.3
No Syst
#
34
System
Name
35
36
37
Part
Part Name
#
6.4 F/R/S Lever
6.5
7
Bit Holder
7.1
7.2
38
7.3
39
7.4
40
41
On/Off Spring
1
Support On/Off
Button
Quantity
Function
Polypropylene
F/R/S Switch
Circuit
Collet
Bit Holder Housing
1
Control polarity connection to battery
1
1
Transmit torque Also to hold bit
Provide housing to drive mechanism
Direction Stopper
Clips
Direction Stoppper
Supports
Screwdriver bit
Planetary Gear 1
(PG1) Washer
PG1/PG3 Pinion
Gears
PG1 Internal Gears
2
Hold PG3 carrier To allow counter rotation
PS
(Polystyrene)
SUM
PS
(Polystyrene)
SUS304
4
Hold stopper
clips
Act on screw
Enclose pinion
gears
Increase torque
PG1 Carrier/PG2
Sun Gear
PG2 Pinion Gears
PG2 Washer
1
PG2 Coupling
Gear
PG2 Locking Gear
1
43
8.3
44
8.4
46
47
8.5
8.6
48
8.7
49
8.8
50
51
8.9 Hi/Lo Lever
8.10 Hi/Lo Button
1
1
52
53
8.11 Hi/Lo Fasteners
8.12 PG2 Carrier/PG3
Sun Gear
8.13 PG3 Washer
2
1
8.14 PG3 Internal
Gear/Direction
Openner
8.15 PG3 Carrier
1
55
56
Material
Provide control for rotation direction
42
54
Note
1
7.5
Transmissi 8.1
on
8.2
8
SUS304
1
1
6
1
3
1
1
1
1
PS
(Polystyrene)
SUM
SUS304
SMF
Coordinate
Allows all pinion gears to rotate SMF
pinion gears
along its internal gear
Hold pinion gears Also transmit torque
SUM
Reduce speed
Enclose pinion
gears
Hold pinion gears
SMF
SUS304
Hold PG2
system
Transmit control By shifting coupling gear
Accept Hi/Lo
control
Hold Hi/Lo lever
Hold pinion gears
Enclose pinion
gears
Coordinate
pinion gears
Hold pinion gears
PS
(Polystyrene)
PS
(Polystyrene)
SUS304
Polypropylene
N?
SUM
SUS304
Allows all pinion gears to rotate SMF
along its internal gear
SUM
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 26 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
2.4. Exploded View
Figure 7. Exploded view of Transmission Sub-assembly.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 27 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3. Report #3: Assembly Sequence
3.1 Revised Liaison Diagram
6. Main Housing
1
6.1 Motor + PG1 Sun Gear
26
27
4
8.3 PG1 Ring Gear
25
8.9 Locking Gear
2
23
8.1 PG1 Washer 24
9
7
8.10 Hi/Lo Lever
7.2 Gear Housing
29
8.2 PG1 Pinion Gears
22
10
8.7 PG2 Washer 21
30
20
6
8.4 PG1 Carrier
19
11
8.8 Coupling Gear
5
8.6 PG2 Pinion Gears
12
18
8.15 PG3 Ring Gear
13
8.13 PG2 Carrier
28
8.14 PG3 Washer
17
14
8.2 PG3 Pinion Gears
3
16
8.16 PG3 Carrier
15
7.1 Shaft
3.2 Revised Datum Flow Chain
6. Main Housing
6
6.1 Motor + PG1 Sun Gear
3
4
6
8.3 PG1 Ring Gear
5
8.9 Locking Gear
6
8.1 PG1 Washer
6
6
8.7 PG2 Washer 3
3
5
8.4 PG1 Carrier
4
4
8.8 Coupling Gear
5
8.2 PG1 Pinion Gears
5
1
5
3
3
8.10 Hi/Lo Lever
7.2 Gear Housing
4
8.6 PG2 Pinion Gears
6
5
8.15 PG3 Ring Gear
3
8.13 PG2 Carrier
3
8.14 PG3 Washer
4
4
8.2 PG3 Pinion Gears
6
5
8.16 PG3 Carrier
6
7.1 Shaft
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 28 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3.3 All Possible Assembly Sequence
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
1
7
13
19
25
2
8
14
20
26
1
7
13
19
25
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
1
7
13
19
25
2
8
14
20
26
3
9
15
21
27
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 29 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
4
10
16
22
28
5
11
17
23
29
6
12
18
24
30
2.875 Mechanical Assembly and Its Role in Product Development
3.4 The Most Conveniencee Assembly Sequence
Transmission/Motor Sub-assembly
R
R
R S F 6. Main Housing
8.12. Fastener for Hi/Lo Lever
8.10. Hi/Lo Lever
6.1. Motor Assembly
8.3. PG1 Ring Gear
8.1. PG1 Washer
Grease
8.2. PG1 Pinion Gears
8.4. PG1 Carrier/PG2 Sun Gear
8.7. PG2 Washer
Grease
F
8.9. PG2 Locking Gear
8.8. PG2 Coupling Gear
8.6. PG2 Pinion Gears
8.13. PG2 Carrier/PG3 Sun Gear
8.14 PG3 Washer
Grease
8.2 PG3 Pinion Gears
F
8.15. PG3 Ring Gear
7.2. Bit Holder Housing
(Including 7.1. Shaft and 8.16. PG3 Carrier)
F: Fixture
S: Snap
: Downward insertion
R: Reorient
F: Remove Fixture
: Horizontal insertion
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 30 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3.5 Required Gross and Fine Motions
Two-digit manual
insertion code
03
04
04
99
03
14
03
03
03
03
99
03
14
03
99
03
13
14
80
02
39
83
8.8
8.9
8.7
8.4
8.2
8.1
8.3
6.1
8.10
8.12
03
05
04
1.95
4
3.6
30
05
04
00
05
05
1.69
30
05
04
1.69
4
3.6
30
05
00
1.69
4
1.13
33
2.51
24
4.35
3.6
1.13
4
4
Figures for
estimation of
theoritical min. of
parts
6
1
1
3
1
1
1
3
1
1
1
1
1
1
3
1
1
1
1
2
1
2
2
31
9
Operation time in
(sec.) = (2)*((4)+(6))
5
7.2
8.15
8.2
4
8.14
8.13
8.6
7
Manual insertion time
per part
4
Manual handling time
per part
Bit Holder Housing (Including Shaft and PG3 Carrier)
PG3 Ring Gear
PG3 Pinion Gears
Grease
PG3 Washer
PG2 Carrier/PG3 Sun Gear
PG2 Pinion Gears
Fixture/Tool (for Hi/Lo lever)
PG2 Coupling Gear
PG2 Locking Gear
Grease
PG2 Washer
PG1 Carrier/PG2 Sun Gear
PG1 Pinion Gears
Grease
PG1 Washer
PG1 Ring Gear
Motor Assembly
Reorientation
Hi/Lo Lever
Snap fit
Fastners (for Hi/Lo lever)
Total
3
Two-digit manual
handling code
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
2
Number of times the
operation is carried
out consecutively
No.
1
Part ID number
Part Name
The Gross and Fine motions are estimated using the Boothroyd & Dewhurst DFA table as
follow.
2
4.5
4.5
12
2
7.5
2
2
2
2
12
2
7.5
2
12
2
5
7.5
9
5.5
3.5
6
3.95
8.5
24.3
12
3.69
11.5
16.8
3.13
6
6
12
3.69
11.5
16.8
12
3.69
9
8.63
18
8.01
7
20.7
226.89
1
1
3
1
0
1
3
0
1
1
0
0
0
0
0
0
0
0
0
1
0
0
13
The Boothroyd and Dewhurst DFA suggest total assembly time of 226.89 seconds or 3
minutes and 46.89 seconds. The actual manual assembly experiments by us took about 4
minutes and 30 seconds without putting any grease.
3.6 Futures, Chamfers and Lead ins
Feature
Number
Part No.
1
7.2
Bit Holder Housing
7.2
Bit Holder Housing
2
3
Part A
8.16 & 7.1 Carrier & Bit Holder
4
8.2
Pinion Gears
5
8.2
Pinion Gears
6
8.15
PG3 Ring Gear
Part No.
Part B
8.16 & Carrier & Bit
7.1 Holder
8.15 PG3 Ring Gear
8.2 Pinion Gears
Chamfers and
Lead-ins
Comments
Not Applicable
Mate(5)
Peg & Hole
N. A.
Mate(5)
Peg & Hole
N. A.
Mate(5)
3 Peg & Holes for 3 pinions
Mate(5)
Over-constrained Dofs, Clearance
Mate(3)
Overlap of 2 plates, Over-Cons.
With #7
Mate(4)
Over-constrained Dofs, Clearance
8.13 PG2 Carrier/PG3 Chamfer and
Sun Gear
Lead-in on all 3
Pinion Gears and
on Sun Gear
8.14 Washer
N. A.
8.2 Pinion Gears
MATE/
CONTACT
Chamfer and
Lead-in on all 3
Pinion Gears and
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 31 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
on Internal Gear
7
8.15
PG3 Ring Gear
8.14 Washer
N. A.
Mate(3)
Overlap of 2 plates, Over-Cons.
With #5
8
8.14
Washer
N. A.
Mate(3)
Overlap of two Plates
9
8.13
N. A.
Mate(5)
3 Peg & Holes for 3 pinions
10
7.2
PG2 Carrier/PG3 Sun
Gear
Bit Holder Housing
N. A.
Mate(5)
Peg & Hole
11
7.2
Bit Holder Housing
8.13 PG2 Carrier/PG3
Sun Gear
8.6 PG2 Pinion
Gears
8.9 PG2 Locking
Gear
8.1 Hi/Lo Lever
N. A.
Mate(5)
Peg & Hole
12
8.6
PG2 Pinion Gears
8.7 PG2 Washer
N. A.
Mate(3)
Overlap of 2 plates, Over-Cons.
With #14
13
8.6
PG2 Pinion Gears
Mate(5)
Over-constrained Dofs, Clearance
14
8.7
PG2 Washer
8.4 PG1 Carrier/PG2 Chamfer and
Sun Gear
Lead-in on all 3
Pinion Gears and
on Sun Gear
8.4 PG1 Carrier/PG2 N. A.
Sun Gear
Mate(3)
Overlap of 2 plates, Over-Cons.
With #12
15
8.6
PG2 Pinion Gears
8.8 PG2 Coupling
Gear
Mate(5)
Over-constrained Dofs, Clearance
16
8.4
3 Peg & Holes for 3 pinions
8.2
Mate(3)
Overlap of 2 plates
18
8.2
PG3 Pinion Gears
Mate(5)
Gear mate
19
8.1
Mate(3)
Overlap of 2 plates
20
8.3
Pinion Gears 1
Washer
PG1 Ring Gear
8.2 PG3 Pinion
Gears
8.1 Pinion Gears 1
N. A.
Washer
4 & 6 Torque Limiter & Chamfer and
Power Generator Lead-in on all 3
Pinion Gears and
on Sun Gear of
Power Generator
8.3 PG1 Ring Gear
N. A.
Mate(5)
17
PG1 Carrier/PG2 Sun
Gear
PG3 Pinion Gears
N. A.
Mate(3)
Overlap of 2 plates
21
8.1
Hi/Lo Lever
N. A.
Mate(1)
22
8.13
PG2 Carrier/PG3 Sun
Gear
4 & 6 Torque Limiter &
Power Generator
8.8 PG2 Coupling
Gear
8.8 PG2 Coupling
Gear
23
8.9
PG2 Locking Gear
8.8 PG2 Coupling
Gear
24
7.2
Bit Holder Housing
25
7.2
Bit Holder Housing
8.8 PG2 Coupling
Gear
8.3 PG1 Ring Gear
26
7.2
Bit Holder Housing
27
8.2
PG3 Pinion Gears
Chamfer and
Lead-in on all 3
Pinion Gears and
on Coupling Gear
N. A.
Chamfer and
Mate(5)
Lead-in on Sun
Gear and on
Coupling Gear
Chamfer and
Mate(6)
Lead-in on Locking
Gear and on
Coupling Gear
N. A.
Mate(3)
Gear mate
N. A.
Mate(3)
Oversize hole
Mate(6)
Properly constrained
Mate(5)
Gear mate
4 & 6 Torque Limiter & N. A.
Power Generator
8.3 PG1 Ring Gear
Chamfer and
Lead-in on all 3
Pinion Gears and
on Internal Gear
Properly constrained
Oversize hole
Description of Chamfers and Lead-ins on Features:
1. Pinion Gears and Sun Gear (Feature #04, #13, #18): Chamfers and Lead-ins are
provided on the Pinion Gears and Gun Gear in order to avoid jamming during
assembly. Once the assembly operations are over, chamfer plays no role.
2. Pinion Gears and Internal Gear (Feature #06, #27): Chamfers and Lead-ins are
provided on the Pinion Gears and Internal Gear to ensure the ease of assembly.
Chamfer plays no role during the actual operation of mechanism.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 32 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3. Pinion Gears and Coupling Gear (Feature #15): Chamfers and Lead-ins avoid the
jamming of these two parts during assembly. They play no role after the product has
been assembled.
4. Sun Gear and Coupling Gear (Feature #22): Here, Chamfers and Lead-ins have
functional importance. The connection between Sun Gear and Coupling Gear is not
permanent. It is established when the Coupling Gear is moved to achieve higher
speed. So, the proper chamfer angle and lead-in are very important. They should be
chosen in such a way that the connection between Sun Gear and Coupling gear is
established irrespective of the angular position of Coupling Gear with respect to Sun
Gear.
5. Coupling Gear and Locking Gear (Feature #00): Here again, Chamfers and Lead-ins
have functional importance. The connection between Locking Gear and Coupling
Gear is established when the Coupling Gear is moved to achieve lower speed.
Coupling Gear and Locking Gear together form the Internal Gear and they act as one
functional unit in this situation. So, the proper chamfer angle and lead-in are very
important. They should be chosen in such a way that the connection between Locking
Gear and Coupling gear is established irrespective of the angular position of Coupling
Gear with respect to Locking Gear.
3.7 Difficulties & Ideas in Assembly
In general, the following alternatives might be considered to eliminate difficult to
assemble parts:
 Modify assembly sequence or architecture to eliminate difficult to access assembly
steps.
 Modify assembly sequence or architecture to reduce lengthy assembly time.
 Examples of the above approaches may lead to the following changes:
 Modify the stacking of planetary gear sets. This step requires architectural changes
as discuss in the next section.
 Commonize and minimize fasteners.
 Eliminate washers.
 Avoid the use of fixtures/tools by finding assembly sequence alternatives.
 Eliminate reorientation by choosing assembly sequence that requires less number
of reorientations.
 Eliminate multiple greasing steps.
The following are some of the possible problems and resolutions.
Liaiso
n#
16
18
Part
A
8.2
8.6
Par
tB
8.1
6
8.1
3
Possible Problems/risks


Possible solutions
Insertion in deep and
narrow hole, blind
operation

Insertion in deep and
narrow hole, blind
operation



Separate 7.2 Bit Holder Housing to two
cylinders
Develop gripper to improve operation (see
fig #5)
Separate 7.2 Bit Holder Housing to two
cylinders
Develop gripper to improve operation (see
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 33 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
27
6.1
8.2

17
8.13
8.2

30
8.8
8.1
0

Need to jiggle the motor

assembly to get proper gear
mating , blind operation
Need to jiggle the motor

assembly to get proper gear
mating
Mating 8.10 to 8.8, because 
8.8 is so free to be
positioned correctly, and
obstructed view
fig #5)
Change the assembly sequence by mating
pinion gears to motor assembly shaft.
Change the assembly sequence by mating
pinion gears to motor assembly shaft.
Use fixture to constrain 8.8, Coupling
gear.
3.8 Feature Parts and Associated Assembly Tool and Fixtures
The insertion tool, T-2, shown in Figure 5.a is used for loading multiple part into the
transmission housing (7.2) during the transmission gear assembly build sequence. The
gripper tool design can be used for loading all pinion carrier gears and ring gears.
The parts in the following table will loaded using T-2.
Subsystem
Transmission
Transmission
Transmission
Transmission
Transmission
Transmission
P/N
8.3
8.4
8.8
8.9
8.13
8.15
Description
PG1 Ring Gears
PG1 Carrier
PG2 Coupling Gear
PG2 Locking Gear
PG2 Carrier
PG3 Ring Gear
Gripping feature
Inside diameter
3 pinion shafts
Inside diameter
Inside diameter
3 pinion shafts
Inside diameter
The T-2 gripping tool is a spreader design. When tool is in a free (un-gripped) state, the
tips of the tool, which contact the part, are in a closed position (see Figure 5.a). This
position is maintained at free state by a spring above the tool pivot point.
When gripping pinion gear carriers, the tool is placed between the 3 pinion gear
pins and loaded until the tool spreads to make sufficient contact (see Figure 5.a).
When gripping ring gears, the tool is placed anywhere on the inside diameter and
loaded until tool spreads to make sufficient contact (see Figure 5.a).
The Pinion Gear Insertion Tool, T-1, shown in Figure 5.b, is used to insert pinion gears
into the transmission housing (7.2). This tool is designed with magnetic inserts placed at
two different depths to allow for diameters and lengths corresponding to both size pinion
gears (8.2 and 8.6). Once the pinion gear has been loaded into the tool and onto a carrier
pin, the button on the top of the tool is pressed by the operator to actuate the ejector pin.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 34 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
This motion extracts the pinion gear from the magnet, leaving it in final assembly
position.
The transmission housing holding fixture, F-1, shown in Figure 5.c holds and orients
the transmission housing (7.2) during transmission assembly buildup. The fixture is hard
mounted to the table in a work-cell in front of the operator. The operator mates the
housing to the fixture by pushing the collet onto a pin at the base of the fixture. Fixturing
the housing prior to gear assembly buildup allows the operator full use of both hands for
loading parts into housing.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 35 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3.9. Fixtures and Tools for Assembly
Figure 5.b. Tool T-1
Figure 5.a. Tool T-2
Figure 5.c. Fixture F-1
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 36 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3.10 Gear Set Architecture Redesign
Original Architecture
Redesigned Architecture
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 37 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
3.11 Improvement highlight
Planetary gear sets are rearranged by moving the Planetary Gear Set #1 next to the
Planetary Gear Set #3. This new architecture results in significant part reduction and part
integration (function sharing, see item #4 below). The redesign also requires some
feature changes as described below.
1. Increasing the length of PG3 ring gear (8.15) to contains both planetary gear #1 and
#3. Significant improvement is achieved by:
 Eliminating PG3 washer (8.14)
 Eliminating locking gear (8.9) by putting its functionality into PG2 Ring Gear
(8.3)
2. Feature modification of PG1 carrier (8.4) to fit PG3 planetary gears and PG3 Ring
gear.
3. Combining the function of locking gear (8.9) into (8.3)
4. Modification of sun gear at the motor shaft to fit PG2 planetary gears (8.6)
5. Shortening the length of bit holder housing (7.2) results the following benefits:
 The assembly of the planetary gear sets #1 and #2 becomes much easier
(eliminating deep insertions)
 Eliminating multiple greasing steps.
The new architecture also provides significant assembly cost benefit by
 Eliminating special tools required in the current design.
 Reduction in the time required assembling the modified product.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 38 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
4. Report #4: Assembly Floor Layout Analysis
The following report steps through the analysis required to propose a feasible plant layout
to effectively perform operations necessary to assembly package and ship the Sears
Craftsman Screwdriver. The team broke the analysis into 3 primary tasks in order to
provide the necessary information for a viable operations solution. These analysis
activities are outlined in the report as follows:
 Assembly Sequence
 Assembly Process time
 Assembly Line Design and Assumptions
4.1. Assembly Sequence
The assembly sequence chosen for the Sears Craftsman Screwdriver are shown in Figures
1 and 2. This sequence was chosen because it was conducive to an efficient flow of
assembly operations that were consistent with the overall operations strategy. The
sequence allowed for easily "chunking" assembly task into workcells that allowed for
optimal assembly line balance. This sequence also allowed the workcell subassemblies to
be robust against damage or loss of parts during transition to downstream operation.
Packed Box
Testing and Packaging
Manual
Testing
Screw Driver
Bits
Final Assembly
Charger Base
1.1:Battery Charger
Cardboard Bin
Drive Housing Fasteners
Box
5.2: Drive Right Housing
5.3: Grip Locking Switch
8.10: High/Lo Button
5.1: Drive Left
Housing
Wire Crimping
6: Motor Assembly
Grip Housing
Battery Assembly
4:Torque Limiter
8:Transmission assembly
Figure 1 – Assembly Sequence Tree
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 39 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 40 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Transmission/Motor Sub-assembly
R
RSF
8.12. Fastener for Hi/Lo Lever
8.10. Hi/Lo Lever
8.3. PG1 Ring Gear
8.1. PG1 Washer
Grease
8.2. PG1 Pinion Gears
8.4. PG1 Carrier/PG2 Sun Gear
8.7. PG2 Washer
Grease
F
8.9. PG2 Locking Gear
8.8. PG2 Coupling Gear
8.6. PG2 Pinion Gears
8.13. PG2 Carrier/PG3 Sun Gear
8.14 PG3 Washer
Grease
8.2 PG3 Pinion Gears
F
8.15. PG3 Ring Gear
7.2. Bit Holder Housing
(Including 7.1. Shaft and 8.16. PG3 Carrier)
F: Fixture
S: Snap
: Downward insertion
R: Reorient
F: Remove Fixture
: Horizontal insertion
Figure 2 -Transmission Sub-Assembly Sequence Tree
4.2 Assembly Process time
Assembly times were determined using Boothroyd & Dewhurst DFA tables (see Figures
3,4,&5). These techniques used associated times correlated to previously determined
manual insertion and handling codes. Once these times were determined, decisions were
made as to what workstations needed to be developed for an optimal work flow and
assembly line balancing. These decisions were also based on product architecture and
interfaces between subsystems, which allow easy and robust transfer to the downstream
workstation.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 41 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
1
1
1
1
1
1
1
1
8
00
03
03
03
00
03
1.13
1.95
1.95
1.95
1.13
1.95
00
1.13
7
Operation time in
(sec.) = (2)*((4)+(6))
6
Manual insertion time
per part
5
Two-digit manual
insertion code
Box
Cardboard bin
Battery Charger
Charger Base
Bits
Screwdriver
Screwdriver testing
Manual
Total
4
Manual handling time
per part
1
2
3
4
5
6
7
8
3
Two-digit manual
handling code
No.
2
Number of times the
operation is carried
out consecutively
Part Name
2.875 Mechanical Assembly and Its Role in Product Development
00
00
00
00
00
30
1.5
1.5
1.5
1.5
1.5
20
31.13
3.45
3.45
3.45
2.63
3.45
20
1.13
68.69
7
1
1
1
1
2
1
1
1
1
6
16
03
01
03
00
1.95
1.13
1.95
1.13
03
13
13
03
10
1.95
2.25
2.25
1.95
1.13
Operation time in
(sec.) = (2)*((4)+(6))
6
Manual insertion time
per part
5
Two-digit manual
insertion code
4
Manual handling time
per part
Transmission Assembly
Torque Limiter
Grip Housing/Battery Assembly
Motor Assembly
Wire Crimping
Drive Left Housing
Hi/Low Button
Grip Locking Switch
Drive Right Housing
Drive Housing Fasteners
Total
3
Two-digit manual
handling code
1
2
3
4
5
6
7
8
9
10
2
Number of times the
operation is carried
out consecutively
No.
Part Name
Figure 3 - Testing and Packaging
20
00
03
2.5
1.5
2
39
03
03
03
03
29
3.5
2
2
2
2
5
4.45
2.63
3.95
1.13
7
3.95
4.25
4.25
3.95
36.78
72.34
Figure 4 - Final Assembly Process Time
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 42 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
4
5
6
Number of times the
operation is carried
out consecutively
Two-digit manual
insertion code
Manual insertion time
per part
Operation time in
(sec.) = (2)*((4)+(6))
Bit Holder Housing (Including Shaft and PG3 Carrier)
PG3 Ring Gear
PG3 Pinion Gears
Grease
PG3 Washer
PG2 Carrier/PG3 Sun Gear
PG2 Pinion Gears
Fixture/Tool (for Hi/Lo lever)
PG2 Coupling Gear
PG2 Locking Gear
Grease
PG2 Washer
PG1 Carrier/PG2 Sun Gear
PG1 Pinion Gears
Grease
PG1 Washer
PG1 Ring Gear
Reorientation
Hi/Lo Lever
Snap fit
Fastners (for Hi/Lo lever)
Total
1
1
3
1
1
1
3
1
1
1
1
1
1
3
1
1
1
2
1
2
2
30
03
04
04
99
03
14
03
03
03
03
99
03
14
03
99
03
13
80
02
39
83
2
4.5
4.5
12
2
7.5
2
2
2
2
12
2
7.5
2
12
2
5
9
5.5
3.5
6
3.95
8.5
24.3
12
3.69
11.5
16.8
3.13
6
6
12
3.69
11.5
16.8
12
3.69
9
18
8.01
7
20.7
218.26
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Manual handling time
per part
3
Two-digit manual
handling code
2
Part Name
2.875 Mechanical Assembly and Its Role in Product Development
03
05
04
1.95
4
3.6
30
05
04
00
05
05
1.69
30
05
04
1.69
4
3.6
30
05
1.69
4
33
2.51
24
4.35
3.6
1.13
4
4
Figure 5 - Transmission Assembly Process Time
It can be seen from the total assembly times found in the above tables that a total process
cycle time of approximately 60-70 seconds should be targeted. The grip housing assembly
process time, although not shown in this report, was calculated using the same method
and found to be approximately 70 seconds. With this information the workstations were
determined to be the following :
Grip Housing Assembly
Transmission Assembly
Final Assembly
Testing and Packaging
(1 workstation)
(3 workstations)
(1 workstation)
(1 workstation)
4.3 Assembly Line Design and Assumptions
Production Volumes were estimated by gathering information about the product
distribution network. This information was found from the Sears website. The table
below summarizes all retail outlets where the products are sold in the 2 key markets of
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 43 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
7
2.875 Mechanical Assembly and Its Role in Product Development
U.S and Canada. Phone surveys were then conducted to gain a reasonable estimate of the
average number of units sold per month at these outlets.
Estimated Sales Amounts
8,358 /month
Estimated Production 379.9 /day (22 working days/month)
SEARS Shops
US
Canada
Department stores
Off-the-mall full-line stores
Subr-lines in rural markets
Full-line stores
Catalog agent & dealers
Total
# of shops
833
1,325
1,384
110
1,550
units/month/
units/month
shop
3
2499
2
2650
1
1384
2.5
275
1
1550
8358
4.3.1 Design Parameters
Considering the estimated production size and the product packaging size, factory-out
distribution of this product will be less than once a day and the batch size should be
defined assembly process.
Parts supply: Parts for one day production are brought to the working area
by full-time worker, who is also responsible to other production
Batch: 95 units (4 batches/ day)
Set-up time 10 min./batch to carry parts from in-house inventory to each
workstation
Working time :7.5 hours/day (actual working time put off recesses)
Assumptive Cycle Time (temporary setting for designing)
Cycle time/ unit
(7.5 hours/day) / (379.9 units/day ) = 71.1 sec.
Cycle time/ batch
(Process time/ # of workers) * (95 units) + 10 min. <
71.1*95 sec.
(1 hours and 53 min., 4 batches/ day)
4.3.2 Supplied Material
It was estimated that supplied materials are all part level and all handicrafts are performed
in house because of following observations:

This product is made in China, in which labor cost is generally low.

Since this product is an integrated product, possible outside sub-assembles are Battery
Assembly and Grip Housing Assembly. However, if these are out-sourced, in
comparison, Transmission Assembly operation requires too long time, even if
separated to two workstation, and other assembly operations become too simple.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 44 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
4.4 Assembly operation style
Given that the annual production volumes were relatively low for a mass production
product and that the assembly operations are in China where labor cost is very low,
automated assembly operations were ruled out as a cost-effective means of assembly.
4.4.1 Assembly Line Design
Considering Assumptive Cycle Time, there is no need to organize highly sequential line,
however, too much individual workstations increase overheads. To balance minimizing
equipment cost and overhead cost, General Assembly Flow becomes as follows:
The production workflow starts with an inventory stockpile that supplies approximately 1
shift of production (see Figure 7 - A). Inventory is transferred manually by laborers to
supply all workcells during the shift. Enough inventory is transferred to workcells to
supply a batch size of 95 units. This is because the space for stocking inventory is limited
at the workcell tables. Also, this allows for the recirculation of the transmission housing
fixtures, which are limited in number to approx. 100 to minimize investment cost (see
line 1 dotted). The details of these fixtures, T-1, are shown in project report #3.
Workcell B assembles the grip housing assembly concurrently with wokcells C,D&E
which assemble the transmissions. These 4 workcells are positioned around a common
conveyor system that feeds into a "pool" for use by the final assembly workcell (F). This
conveyor system consists of an inclined set of rollers or possibly a steel chute. It is
approximately 6 meters in length, so an automated transfer system is not necessary. It is
important to note that 3 workcells were used to assemble the transmissions to achieve
proper assembly line balancing. This strategy was needed because cycle time for
transmission assembly was 185 seconds (218 sec. without tool efficiency, see Figure 6).
By having 3 workcells the combined cycle time becomes 62 seconds. This is less than the
72 seconds required for final assembly, which will prevent build up of inventory.
Note: Holding fixtures are used to hold the transmission gear assembly vertical. These
fixture are placed on the conveyor along with assembled workpiece. After going through
final assembly, these fixtures are recirculated to workcells C,D, and E by a manual labor
head.
Workcell F is the place for final assembly. The transmission assembly is picked up and
motor is assembled with it. The grip housing assembly is picked up next and it is
assembled with it. Other part of the housing is snap fitted on to rest of the sub-assembly.
Workcell G stores the fixtures being used in the transmission assembly These fixtures are
sent back to the workcells C,D and E.
Workcell H is for packaging and testing. The fully assembled screwdrivers are picked
from workcell G and they are tested both in high speed and low speed operating
conditions.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 45 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Supplied Once a day
In-house
Material
Inventory
Set-up Time: 10 min./Batch
Grip Housing
Assembly
Carried Once
In-house a day Out-house
Testing &
Packaging
Final Assembly
Transmission
Assembly
Cycle Time: about 62 sec.
Cycle Time : about 72.34 sec.
1 worker for Grip Housing
1 worker
3 workers for Transmission
(Process Time:218.26--> 185 sec. by 15% tool efficiency)
Inventory
Inventory
Cycle Time : about 68.69 sec.
1 worker
Figure 6 –Assembly Flow Diagram
Packaging & Testing
H
Final Assembly
G
Storage for
Trans.
Housing
Fixture Tool
Parts Pallet
Parts Shelf
F
Parts Shelf
Table
Table
Once a day
by Forklift
In-house Inventory
for Final Assembly
(Pallet)
Slider
Pool
Pool
J
D
Parts Shelf
Parts Shelf
Table
A
Once a day
by Forklift
In-house Material
Inventory
(Containers on Pallet)
E
C
Transmission
Assembly-1
Table
Parts Shelf
Closer position for heavier parts
1 m2
Grip Housing
Assembly
Table
Conveyor
Transmission
Assembly-2
B
Transmission
Assembly-3
Assembly Sequence
Material Supply
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 46 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Figure 7 –Floor Layout
Materials are ordered Right to Left
along assembly sequence
Materials are supplied from rear side
Tools & Grease-gun Hang Wall
Parts Shelf
Work Table
Small materials are
automatically supplied
on the table
Conveyer is located light-hand
Figure 8 –Workstation table Design
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 47 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 48 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
5. Report #5: Workstation Design
5.1 Required cycle time to complete the planned operations
Following Assembly Flow Diagram shows cycle time for all the operations involved in
screwdriver sub-assemblies, final assembly and testing/packing. For more details please
refer to individual charts.
5.1.1 Assembly Flow Diagram
Supplied Once a day
In-house
Material
Inventory
Set-up Time: 10 min./Batch
Grip Housing
Assembly
Final Assembly
Transmission
Assembly
Cycle Time: about 62 sec.
Cycle Time : about 72.34 sec.
1 worker for Grip Housing
1 worker
3 workers for Transmission
(Process Time:218.26--> 185 sec. by 15% tool efficiency)
Testing &
Packaging
Carried Once
In-house a day Out-house
Inventory
Inventory
Cycle Time : about 68.69 sec.
1 worker
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 49 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Manual insertion time
per part
Operation time in
(sec.) = (2)*((4)+(6))
20
00
03
2.5
1.5
2
1.95
2.25
2.25
1.95
1.13
39
03
03
03
03
29
3.5
2
2
2
2
5
4.45
2.63
3.95
1.13
7
3.95
4.25
4.25
3.95
36.78
72.34
3
4
5
6
Manual insertion time
per part
Operation time in
(sec.) = (2)*((4)+(6))
7
Two-digit manual
insertion code
6
Two-digit manual
insertion code
5
00
00
00
00
00
30
1.5
1.5
1.5
1.5
1.5
20
31.13
3.45
3.45
3.45
2.63
3.45
20
1.13
68.69
Manual handling time
per part
Transmission Assembly
Torque Limiter
Grip Housing/Battery Assembly
Motor Assembly
Wire Crimping
Drive Left Housing
Hi/Low Button
Grip Locking Switch
Drive Right Housing
Drive Housing Fasteners
Total Time
4
Two-digit manual
handling code
1
2
3
4
5
6
7
8
9
10
3
Number of times the
operation is carried
out consecutively
No.
2
1
1
1
1
2
1
1
1
1
6
16
03
01
03
00
1.95
1.13
1.95
1.13
03
13
13
03
10
2
Number of times the
operation is carried
out consecutively
Part Name
5.1.2 Final Assembly
1
2
3
4
5
6
7
8
Box
Cardboard bin
Battery Charger
Charger Base
Bits
Screwdriver
Screwdriver testing
Manual
Total Time
1
1
1
1
1
1
1
1
8
Manual handling time
per part
No.
Two-digit manual
handling code
Part Name
5.1.3 Testing and Packaging
00
03
03
03
00
03
1.13
1.95
1.95
1.95
1.13
1.95
00
1.13
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 50 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
7
2.875 Mechanical Assembly and Its Role in Product Development
5.1.4 Transmission Assembly
Manual insertion time
per part
Operation time in
(sec.) = (2)*((4)+(6))
3
4
5
6
7
Manual insertion
time per part
1
1
1
4
1
1
1
2
12
03
00
03
00
02
03
00
10
1.95
1.13
1.95
1.13
1.8
1.95
1.13
1.13
03
00
00
59
3
03
00
29
2
1.5
1.5
8
2
2
2
5
Manual handling time
per part
3.95
8.5
24.3
12
3.69
11.5
16.8
3.13
6
6
12
3.69
11.5
16.8
12
3.69
9
18
8.01
7
20.7
218.26
Two-digit manual
handling code
2
4.5
4.5
12
2
7.5
2
2
2
2
12
2
7.5
2
12
2
5
9
5.5
3.5
6
Number of times the
operation is carried
out consecutively
4.35
03
04
04
99
03
14
03
03
03
03
99
03
14
03
99
03
13
80
02
39
83
Part Name
Two-digit manual
insertion code
7
Two-digit manual
insertion code
6
Manual handling
time per part
5
Two-digit manual
handling code
4
Number of times
the operation is
carried out
consecutively
3
Bit Holder Housing (Including Shaft and PG3 Carrier)
PG3 Ring Gear
PG3 Pinion Gears
Grease
PG3 Washer
PG2 Carrier/PG3 Sun Gear
PG2 Pinion Gears
Fixture/Tool (for Hi/Lo lever)
PG2 Coupling Gear
PG2 Locking Gear
Grease
PG2 Washer
PG1 Carrier/PG2 Sun Gear
PG1 Pinion Gears
Grease
PG1 Washer
PG1 Ring Gear
Reorientation
Hi/Lo Lever
Snap fit
Fastners (for Hi/Lo lever)
Total Time
1
1
3
1
1
1
3
1
1
1
1
1
1
3
1
1
1
2
1
2
2
30
03
05
04
1.95
4
3.6
30
05
04
00
05
05
1.69
30
05
04
1.69
4
3.6
30
05
1.69
4
33
2.51
24
2
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
2
3.6
1.13
4
4
No.
1
2
3
4
4
5
6
8
Left Housing
Battery Package
Switch circuit
Wiring
Switch button
Right Housing
Closure
Fasteners
Total Time
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 51 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
Operation time in
(sec.) = (2)*((4)+(6))
Part Name
5.1.5 Grip Housing/Battery Assembly
3.95
2.63
3.45
36.52
3.8
3.95
3.13
12.26
69.69
2.875 Mechanical Assembly and Its Role in Product Development
It can be seen from the total assembly times found in the above tables that a total process
cycle time of approximately 60-70 seconds should be targeted. With this information the
workstations were determined to be the following:
Grip Housing Assembly
Transmission Assembly
Final Assembly
Testing and Packaging
(1 workstation)
(3 workstations)
(1 workstation)
(1 workstation)
Tr1: Transmission Assembly Workstation #1:
Tr2: Transmission Assembly Workstation #2:
61.84 sec.
Tr3: Transmission Assembly Workstation #3:
Bat: Grip Housing/Battery Assembly Workstation:
69.69 sec.
Fin: Final Assembly Workstation:
72.34 sec.
T&P: Testing and Packaging Workstation:
68.69 sec.
Inp: Input Component Inventory, Out: Finished Good Inventory



= (Analyzed assembly time
218.26 sec.)
* (1 - tool efficiency 15%)
/ (3 workstations)
We have provided a small buffer (storage) between workstations to protect for
process uncertainties, therefore the cycle time of assembly line is directly obtained as
a longest cycle time among workstations.
Cycle Time of Assembly Line = 72.34 sec.
Critical Workstation is Final Assembly, which is located the second sequence
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 52 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
5.2 Station lay out: in and out flows of assemblies and parts
In this report we are focusing on "Transmission assembly". The workstation layout and
other details are shown in following diagrams.
Workstation table Design
Materials are ordered Right to Left
along assembly sequence
Materials are supplied from rear side
Parts Shelf
Work Table
Small materials are
automatically supplied
on the table
Conveyer is located light-hand
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 53 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
7.2
B it H o ld e r H o u s in g
8.1
P la n e t a ry G e a r 1 W a s h e r
8.2
P G 1 P in io n G e a rs
8.3
P G 1 In t e rn a l G e a rs
8.4
P G 1 C a rrie r
8.6
P G 2 P in io n G e a rs
8.7
P G 2 W as her
8.8
P G 2 C o u p lin g G e a r
8.9
P G 2 L o c k in g G e a r
Transmission Workstation
F-1 Stacked on spring loaded riser
Fixtures enter onto Angled Chute
8.14
8 . 1 3 P G 2 C a rrie r
8.7
8.14 P G 3 W as her
8 . 1 5 P G 3 In t e rn a l G e a r
8.1
8.8
8.2
8.15
8.6
8.9
8.3
8.4
8.13
Load stock here
Grease Gun
Operator Grabs parts
from here
Conveyor
T-1, Insertion Tool
T-2, Insertion Tool
7.2
1 sq. ft.
Operator
5.3 Required motions of equipment and people
Evaluation of required motions according to various criteria is very important in manual
assembly. The criteria can be summarized under following topics:
Right and left hand should be operative for the same amount of time.
Motions of right and left hand should be synchronized. I.e. the motions of right and left
hand should be in succession.
The arm movement should be minimized. The maximum movement of arm should be
with in the reach of operator.
The movement of the operator in the workstation area should be minimized.
Parts should be placed in bins in such a way that they can be picked by the operator in
correct orientation without any difficulty. I.e. parts should not entangle with themselves
in the bins.
These are some of the rules of “motion and time study” which have been given attention
while designing the “transmission workstation”. The slides show the configuration of the
workstation. Following is the brief summary of the hand motions:
The initial step for the operator is to place the transmission holding fixture (F-1) on the
table in front of himself. These fixtures are supplied from the other side of the table
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 54 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
where they are loaded onto a spring-loaded riser that feeds the fixtures down an angled
chute. These fixtures are continuously being circulated from the final assembly
workstation where the finished transmission assembly is removed from the fixture.
Pick up the Bit Holder Housing (BH Housing 7.2) from right hand and shift it to the left
hand.
Pick up the T-1 Insertion Tool with right hand.
Pick up PG1 Internal Gear (8.3) with the help of T-1 insertion tool with right hand while
putting the BH Housing (7.2) in the Fixture with left hand.
Insert the PG1 Internal Gear (8.3) in the BH Housing (7.2) with right hand.
Put the T-1 Insertion Tool down and pick T-2 Insertion Tool in right hand.
Pick up the PG1 Pinion Gears (8.2) with the help of T-2 Insertion tool and insert them
one by one with right hand.
Pick up the Grease Gun in the left hand and put grease in the sub-assembly.
Pick up the PG1 Washer (8.1) with left hand and drop it in the BH Housing (7.2).
Pick up the PG1 Carrier (8.4) with the help of T-2 Insertion tool with right hand and
insert it.
Pick up PG2 Pinion Gears (8.6) with the help of T-2 Insertion Tool and insert them one
by one.
Pick up PG2 Coupling Gear (8.8) with the left hand, grip it with T-2 Insertion Tool and
insert it.
Pick up PG2 Locking Gear (8.9) with the right hand, grip it with T-2 Insertion Tool and
insert it.
Pick up the Grease Gun in the left hand and put grease in the sub-assembly.
Pick up the PG2 Washer (8.7) with left hand and drop it in the BH Housing (7.2).
Pick up the PG2 Carrier (8.13) with the help of T-2 Insertion Tool with right hand and
insert it.
Pick up PG3 Pinion Gears (8.6) with the help of T-2 Insertion tool and insert them one by
one.
Pick up the PG3 Washer (8.14) with left hand and drop it in the BH Housing (7.2).
Pick up the PG3 Internal Gear with left hand and drop it in the BH Housing (7.2).
These are the steps required for the assembly process. Both of the hands have been used
intermittently. This sequence has been developed by assuming that the operator is lefthanded. If this is not the case, one needs to simply shift the bins on the right to the left
and vice-versa. The jobs assigned to the right hand will then be done by left hand. The
motion has been kept as synchronized as possible. More importantly, the location of
feeder bins containing the Pinion Gears has been designed very close to the right hand of
the operator because there are nine pinion gears in total in the part.
Finally, the operator needs to put the finished sub-assembly along with the fixture on the
conveyor.
5.4 Necessary inspections or tests
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 55 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Screwdriver testing is done as a part of testing and packaging operation. We decided to
test fully assembled screwdriver at "Packaging" station in order to balance times on the
assembly line. The testing involves following steps:
The fully assembled screwdrivers are picked from workcell
Test high speed and low speed operating conditions
Test Forward and Reverse feature
Test Adjustable Torque feature (Torque Limiter)
Test dual-position handle and pistol-grip lock feature
After passing the test they are placed in cardboard bin (screwdrivers which fail are kept in
a "rework" bin.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 56 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
5.5 Gantt chart of required time of activities and a complete
cycle
The complete assembly process is shown in the following diagram where the sequence is
bottom-up. The assembly sequence was then broken down in to specific assembly activity
steps and a "Gantt" charts were created.
Packed Box
Testing and Packaging
Manual
Testing
Screw Driver
Bits
Final Assembly
Charger Base
1.1:Battery Charger
Cardboard Bin
Drive Housing Fasteners
Box
5.2: Drive Right Housing
5.3: Grip Locking Switch
8.10: High/Lo Button
5.1: Drive Left
Housing
Wire Crimping
6: Motor Assembly
Grip Housing
Battery Assembly
4:Torque Limiter
8:Transmission assembly
Assembly sequence
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 57 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Assembly process design mainly follows 1) required cycle time, which is obtained from
planned production size, 2) modularity, the mass of assembly sequence which is difficult
to be separated, 3) efficiency in assembly motions and equipment cost.
In this case, we designed the assembly process from following observations:
Required Cycle Time
As shown in the last report, planned production size is 8358 units/month, therefore;
(7.5 hours/day) / (379.9 units/day) = 71.1 sec.
Modularity
Transmission Assembly is toughly integrated and hard to separate to two or more
workstations. Estimated assembly time for this module is 218 sec., which is
approximately three times of Required Cycle Time.
Efficiency
One thought to solve modularity problem in Transmission Assembly is organizing three
parallel lines all of which perform full assemble sequence.
In this case, estimated impact on the equipment cost is small since our assumption of line
designing is full handcraft line. However, motional efficiency must be worse since small
motions, for example, transmission assembly, and large motions, for example, packaging
and carrying the packaged products to the storage, are combined in each workstation.
Finally, we used following logic to design the assembly process:
Organize three transmission assembly workstations to meet Required Cycle Time.
Organize packaging workstation to separate large motions from small assembly motions.
Organize workstations gathering other activities to meet Required Cycle Time.
The designed assembly process logic is shown in the following figure. For cycle time
calculations please refer to section 5.1.
Tr1
Tr2
Inp
Tr2
Fin
T&P
Out
Bat
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 58 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
The timing of the process is shown in the following Gantt chart.
Transmission Assembly
1
2
3
4
5
6
7
8
Station 1
T1
T4
T7
Station 2
T2
T5
T8
Station 3
T3
T6
Grip Housing/Battery Assembly
Final Assembly
Testing and Packaging
B1
B2
B3
9
10
T9
B4
B5
B6
F1(T1,B1) F2(T2,B2) F3(T3,B3) F4(T4,B4) F5(T5,B5) F6(T6,B6)
P1(F1)
P2(F2)
P3(F3)
P4(F4)
P5(F5)
Where
T1: Transmission Assembly #1, T2: Transmission Assembly #2, …
B1: Battery Housing Assembly #1, B2: Battery Assembly #2, …
F1: Final Assembly #1, F2: Final Assembly #2, …
P1: Testing and packaging #1, P2: Testing and packaging #2, …
Where the detailed subprocesses is shown in the following Gantt charts. The timing scale
is shown in seconds.
Final Assembly Timing
Testing and Packaging Timing
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 59 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
P6(F6)
2.875 Mechanical Assembly and Its Role in Product Development
Transmission Assembly Timing
Grip Housing/Battery Assembly Timing
The timing represented in the above Gantt chart is acquired from motion and time study
using Boothroyd & Dewhurst's DFA database as shown in the tables in section 5.1.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 60 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
5.6 Cost estimation of workstations
The screwdriver assembly line consists of standard equipment except small parts cases.
The estimated purchase and installation costs are as follows:
#
Equipment
units
Transmission Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
5 Parts Case
11
6 Insertion Tool (T-1)
1
7 Insertion Tool (T-2)
1
8 Grease Gun
1
9 Housing Fixture
100
Workstation Total
3
3 Workstations Total
Grip Housing Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
5 Parts Case
12
6 Plier
1
7 Electoric Driver
1
Workstation Total
Final Assembly Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
5 Parts Case
8
6 Plier
1
7 Electoric Driver
1
Workstation Total
Final Assembly Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
Workstation Total
Common
1 Conveyor
1
2 Slider
1
3 Pooling Table
3
4 Fixture Storage Box
1
6 Parts Carrier
2
5 Spare Tools
1set
Ground Total
Purchase
Cost ($)
Making Cost
($)
Installing
Cost ($)
150
18
30
200
40
80
80
50
15
15
150
18
30
200
40
50
3
40
150
18
30
200
40
3
40
50
Sub Total ($)
150
18
30
200
490
80
80
15
1500
2563
7689
150
18
30
200
530
3
40
971
150
18
30
200
370
3
40
811
150
18
30
600
150
18
30
600
798
2000
500
15
20
30
2000
500
45
20
60
160
13054
160
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 61 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
5.7 Estimation of the cost of performing one assembly cycle
Original assembly cycle time and cost to perform one assembly are obtained using
following formula:
(Transmission AT+Grip Housing AT+Final AT+Packaging & Testing AT)*Labor
Rate
=
=
=
(218.26*85% + 69.69 + 72.34 + 68.69)*(1/3600)*@1.3
(396.24 sec.)*(1/3600)*@1.3
$0.143
where;
AT: Assembling Time
1/3600:
Seconds to hours translation
85%: 15% tool efficiency
@1.3: $1.3/hour Chinese labor rate
However, actual assembling cost follows Cycle Time of Assembly Line, and it’s obtained
with following formula:
=
=
=
(Longest Cycle Time)*(# of Workers)*Labor Rate
(72.34)*6*(1/3600)*@1.3
(434.04 sec.)*(1/3600)*@1.3
$0.157
Where, the overhead of designed assembly line to the ideal assembly is 9.5%.
= (434.04 – 396.24) / 396.24
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 62 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
6. Report #6: Economic Analysis and Assembly Line Simulation
6.1 Economic analysis of this assembly layout
As shown in following table this assembly line consists of standard equipment except
small parts cases. The estimated purchase and installation costs are as follows:
Transmission Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
5 Parts Case
11
6 Insertion Tool (T-1)
1
7 Insertion Tool (T-2)
1
8 Grease Gun
1
9 Housing Fixture
100
Workstation Total
3
3 Workstations Total
Grip Housing Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
5 Parts Case
12
6 Plier
1
7 Electoric Driver
1
Workstation Total
Final Assembly Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
5 Parts Case
8
6 Plier
1
7 Electoric Driver
1
Workstation Total
Final Assembly Workstation
1 Table
1
2 Side Desk
1
3 Chair
1
4 Parts Self
1
Workstation Total
Common
1 Conveyor
1
2 Slider
1
3 Pooling Table
3
4 Fixture Storage Box
1
6 Parts Carrier
2
5 Spare Tools
1set
Total
150
18
30
200
40
80
80
50
15
15
150
18
30
200
40
50
3
40
150
18
30
200
40
3
40
50
150
18
30
200
490
80
80
15
1500
2563
7689
150
18
30
200
530
3
40
971
150
18
30
200
370
3
40
811
150
18
30
600
150
18
30
600
798
2000
500
15
20
30
2000
500
45
20
60
160
13054
160
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 63 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
(Equipment and Installation costs) / (Production amount: units/year)*(5 years)
= $13,054/((6,490 units/month)*(12 months)*(5 years))
= $0.0202 per unit
*1: This 5 years is an assumptive lifecycle of this product, and means that this
equipment is used only for this product, even though many of equipment are
reusable to other products.
6.1.1 Estimated Manufacturing Cost
Assembling cost follows Cycle Time of Assembly Line and Set-up Time, which is needed
for every batch to supply materials. This cost is calculated with following formula:
=
=
=
((Longest Cycle Time)*(# of Workers) + (Set-up Time)/(Batch size))*Labor Rate
(72.34)*6*(1/3600)*@1.3
((434.04 sec.)*(1/3600) +((15 min.)/(95 units))*(1/60))*@$1.3
$0.1601 per unit
where;
1/3600:
Seconds to hours translation
1/60: minutes to hours translation
@$1.3: $1.3/hour Chinese labor rate
Adding on this, we assume success rate of assembly line to 95% including spec out
assembly, equipment down time, and operational delay.
Therefore, actual assembly cost is:
=
$0.1601/0.95
$0.1685 per unit
Furthermore, managing costs are usually required to design the assembly line and handle
the products. If we suppose that 0.1 manpower/day, whose labor rate is $3.5, is required
in average for this product, the managing cost becomes as follows:
=
=
((Required managing manpower/day)*(Labor Rate)*(Working hours))
/ (Daily production amounts)
((0.1 man/day)*@$3.5*6.93)/((6490 units/month)/(22 working days/month)
$0.0157 per unit
where;
working hours =(72.34sec/unit)*(295units/day)+(15min)*(4batchs) = 6.93
We don’t include other costs such as land space cost or indirect stuff cost to the
manufacturing costs.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 64 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
6.1.2 Inventory Cost and Distribution Cost
As we mentioned in previous report, this manufacturing system includes in house
inventories for materials and finished products.
And, of course, distribution cost is also required to supply products to SEARS shops.
However we directly assume these costs as follows since it’s quite difficult to estimate all
numbers relating to these factors reasonably.
Material inventory cost:
Finished product inventory cost:
Distribution cost:
$0.01 per unit
$0.03 per unit
$0.60 per unit (primarily shipping cost from China to U.S)
6.1.3 Development Cost
We assume that this product was designed in the U.S. under the following conditions:
Engineers:
Engineering labor rate:
Duration:
Prototype modeling cost:
2 people
$10,000 /man-month
6 month (including from concept designing to drawing)
$3,000
The development cost per unit is calculated as follows:
=
((2 engineers)*(6 month)*($10,000 /man-month) + $3,000)
/ ((6,490 units/month)*(12 months)*(5 years))
$0.3546 per unit
We don’t consider other costs as follows:
Designing equipment cost, including housing, energy, and devices such as CAD
Managing cost
Indirect stuff cost
Designing supply chain cost, such as negotiating with suppliers and establishing delivery
route
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 65 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
6.1.4 Unit Part Costs
No. System #
1
0
2
3
4
1
5
2
6
7
8
9
10
3
11
12
13
14
15
16
17
18
4
19
20
21
22
23
24
25
26
27
5
28
29
30
31
32
33
34
6
35
36
37
38
39
7
40
41
42
43
44
8
45
46
47
48
49
50
51
52
53
54
55
56
57
58
System Name
Packaging
Battery Charger
Battery Closure
Power Storage
Torque Limiter
Drive Closure
Power generator
Bit Holder
Transmission
Part #
0.1
0.2
0.3
1.1
2.1
2.2
2.3
2.4
2.5
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5.1
5.2
5.3
5.4
5.5
5.6
5.7
6.1
6.2
6.3
6.4
6.5
7.1
7.2
7.3
7.4
7.5
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10
8.11
8.12
8.13
8.14
8.15
Part Name
Box
unit cost
Qty. Total
Function
0.075
1
0.075
Cardboard bin
0.01
1
0.01
Manual
0.02
1
0.02
0.4
1
0.4
Charge Battery
0.005
0.01
Contact Power
0.15
2
1
0.15
Enclose Battery
Bettery Right Housing
0.15
1
0.15
Enclose Battery
Battery Cover
0.05
1
0.05
Enclose Battery
0.0025
2
0.005
Hold battery housing
0.3
3
0.9
0.004
2
0.008
Transmit power
0.01
2
0.02
Connect cable
0.1
2
0.2
Transmit power
0.01
2
0.02
Hold cable
Shrink wrap
0.0015
1
0.0015
Hold batteries
Tape
0.0015
1
0.0015
Hold cable
Cable connectors
0.015
2
0.03
Connect cables to battery
Torque Limiter Outer Cap
0.175
1
0.175
Accept hand
Torque Limiter Inner Cap
0.175
1
0.175
Accept outer cap
Torque Limiter Cap Clip
0.025
1
0.025
Hold inner and outer caps
Needle Bearings
0.015
4
0.06
Push PG1 internal gear
Ball Bearings
0.015
6
0.09
Allow internal gear PG1 slippage
Bearing holder plate
0.05
1
0.05
Hold ball bearings
Torque Limiter Springs
0.01
4
0.04
Hold bearing holder plate
Torque Limiter Base Support
0.09
1
0.09
Support springs
Torque Limiter Fasteners
0.005
2
0.01
Hold base support to motor
Drive Left Housing
0.375
1
0.375
Provide enclosure to drive
Drive Right Housing
0.375
1
0.375
Provide enclosure to drive
Grip Locking Switch
0.1
1
0.1
Hold grip position
Grip Locking Spring
0.01
1
0.01
Support grip locking switch
Drive Housing Long Fasteners
0.01
2
0.02
Hold housing
Drive Housing Medium Fasteners
0.01
2
0.02
hold drive
Drive Housing Short Fasteners
0.01
2
0.02
hold housing
DC Motor
1.25
1
1.25
Convert EE to Kinetic Energy
On/Off Button
0.09
1
0.09
Connect electric power
On/Off Spring
0.01
1
0.01
Support On/Off Button
F/R/S Lever
0.04
1
0.04
Provide control for rotation direction
0.4
1
0.4
Control polarity connection to battery
0.325
1
0.325
0.4
1
0.4
Provide housing to drive mechanism
0.025
2
0.05
Hold PG3 carrier
Direction Stoppper Supports
0.02
4
0.08
Hold stopper clips
Screwdriver bit
0.04
2
0.08
Act on screw
Planetary Gear 1 (PG1) Washer
0.02
1
0.02
Enclose pinion gears
PG1/PG3 Pinion Gears
0.05
6
0.3
Increase torque
0.1
1
0.1
Coordinate pinion gears
PG1 Carrier/PG2 Sun Gear
0.11
1
0.11
Hold pinion gears
PG2 Pinion Gears
0.06
3
0.18
Reduce speed
0.015
1
0.015
Enclose pinion gears
PG2 Coupling Gear
0.14
1
0.14
Hold pinion gears
PG2 Locking Gear
0.115
1
0.115
Hold PG2 system
Hi/Lo Lever
0.04
1
0.04
Transmit control
Hi/Lo Button
0.06
1
0.06
Accept Hi/Lo control
Hi/Lo Fasteners
0.01
2
0.02
Hold Hi/Lo lever
0.125
1
0.125
Hold pinion gears
0.02
1
0.02
Enclose pinion gears
PG3 Internal Gear/Direction Openner
0.225
1
0.225
Coordinate pinion gears
PG3 Carrier
0.175
1
0.175
Hold pinion gears
Battery Charger
Charger Contact Plates
Battery Left Housing
Baterry Housing Fasteners
Rechargable Batteries
Battery Cables
Battery Connectors
Switch to Motor Cables
Crim Connectors
F/R/S Switch Circuit
Collet
Bit Holder Housing
Direction Stopper Clips
PG1 Internal Gears
PG2 Washer
PG2 Carrier/PG3 Sun Gear
PG3 Washer
TOTAL =
Store power
Transmit torque
8.056 $
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 66 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
6.1.5 Economic Analysis
The engineering economic analysis for the payback period and Internal Rate of Return is
shown in the following table. Since the process is a manual operation with minimum
initial investment cost, the analysis indicates a very favorable result in terms of payback
period (9 months) and IRR (21.5%).
Production Volume =
Product Life Cycle=
Product Unit Price=
Fixed Costs
Tooling & Facilites
Prototype Modeling
6490
5
15
units/month
yrs
$
Fixed Cost
Month (investment)
13054
3000
In 4th month
Development Costs (man-months, 6 mon PD cycle)
Engineering Labor
20000 /month
Variable Costs
Manufacturing(Labor)
Management (Labor)
Purchased Parts
Raw Mat'l Inv
Finished Product Inv
Distribution
Total
Discount Rate= 15.00%
per unit
0.168526
0.0157
8.06
0.01
0.03
0.6
8.884226
apr
IRR =
1.2500%
monthly rate
Variable
Cost
Revenue
Payback in
Net Cost
21.5%
9
NPV =
1,455,526
Discount
Factor PV month Cumulitive
1
-20000
-20000
0.9877
-19753.09
-19753.09
2
-20000
-20000
0.9755
-19509.22
-39262.31
3
-20000
-20000
0.9634
-19268.37
-58530.67
4
-23000
-23000
0.9515
-21885.06
-80415.73
5
-20000
-20000
0.9398
-18795.54
-99211.27
6
-33054
-57658.63
97350
6637
0.9282
6160.64
-93050.63
7
-57658.63
97350
39691
0.9167
36385.71
-56664.92
8
-57658.63
97350
39691
0.9054
35936.51
-20728.41
9
-57658.63
97350
39691
0.8942
35492.85
14764.43
10
-57658.63
97350
39691
0.8832
35054.66
49819.09
11
-57658.63
97350
39691
0.8723
34621.89
84440.98
12
-57658.63
97350
39691
0.8615
34194.46
118635.44
13
-57658.63
97350
39691
0.8509
33772.30
152407.74
14
-57658.63
97350
39691
0.8404
33355.36
185763.10
15
-57658.63
97350
39691
0.8300
32943.57
218706.67
16
-57658.63
97350
39691
0.8197
32536.86
251243.53
17
-57658.63
97350
39691
0.8096
32135.17
283378.70
18
-57658.63
97350
39691
0.7996
31738.44
315117.13
19
-57658.63
97350
39691
0.7898
31346.60
346463.74
20
-57658.63
97350
39691
0.7800
30959.61
377423.34
21
-57658.63
97350
39691
0.7704
30577.39
408000.74
22
-57658.63
97350
39691
0.7609
30199.89
438200.63
23
-57658.63
97350
39691
0.7515
29827.05
468027.68
24
-57658.63
97350
39691
0.7422
29458.82
497486.50
25
-57658.63
97350
39691
0.7330
29095.13
526581.63
26
-57658.63
97350
39691
0.7240
28735.93
555317.56
27
-57658.63
97350
39691
0.7150
28381.17
583698.73
28
-57658.63
97350
39691
0.7062
28030.78
611729.51
29
-57658.63
97350
39691
0.6975
27684.72
639414.23
30
-57658.63
97350
39691
0.6889
27342.94
666757.17
31
-57658.63
97350
39691
0.6804
27005.37
693762.54
32
-57658.63
97350
39691
0.6720
26671.97
720434.51
33
-57658.63
97350
39691
0.6637
26342.69
746777.19
34
-57658.63
97350
39691
0.6555
26017.47
772794.66
35
-57658.63
97350
39691
0.6474
25696.26
798490.93
36
-57658.63
97350
39691
0.6394
25379.03
823869.95
37
-57658.63
97350
39691
0.6315
25065.70
848935.66
38
-57658.63
97350
39691
0.6237
24756.25
873691.91
39
-57658.63
97350
39691
0.6160
24450.62
898142.53
40
-57658.63
97350
39691
0.6084
24148.76
922291.29
41
-57658.63
97350
39691
0.6009
23850.63
946141.91
42
-57658.63
97350
39691
0.5935
23556.17
969698.09
43
-57658.63
97350
39691
0.5862
23265.36
992963.45
44
-57658.63
97350
39691
0.5789
22978.13
1015941.58
45
-57658.63
97350
39691
0.5718
22694.45
1038636.03
46
-57658.63
97350
39691
0.5647
22414.27
1061050.30
47
-57658.63
97350
39691
0.5577
22137.55
1083187.85
48
-57658.63
97350
39691
0.5509
21864.25
1105052.10
49
-57658.63
97350
39691
0.5441
21594.32
1126646.42
50
-57658.63
97350
39691
0.5373
21327.72
1147974.15
51
-57658.63
97350
39691
0.5307
21064.42
1169038.56
52
-57658.63
97350
39691
0.5242
20804.36
1189842.93
53
-57658.63
97350
39691
0.5177
20547.52
1210390.45
54
-57658.63
97350
39691
0.5113
20293.85
1230684.30
55
-57658.63
97350
39691
0.5050
20043.31
1250727.60
56
-57658.63
97350
39691
0.4987
19795.86
1270523.46
57
-57658.63
97350
39691
0.4926
19551.46
1290074.92
58
-57658.63
97350
39691
0.4865
19310.09
1309385.01
59
-57658.63
97350
39691
0.4805
19071.69
1328456.70
60
-57658.63
97350
39691
0.4746
18836.24
1347292.94
Months
$
Payback
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 67 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
6.2 Discrete event simulation of assembly line
6.2.1 Discrete Event Simulation: Configuration Study
The simulation layout for the complete screwdriver assembly is shown in the following
figure.
Transmission
Assembly 1
In 1
Buffer 1
Transmission
Assembly 2
Buffer 3
Transmission
Assembly 3
Final
Assembly
In 2
Buffer 2
Grip Housing
Assembly
Buffer 5
Test &
Packaging
Buffer 4
Buffer 6
Repair
From previous report, it is estimated that the required assembly cycle is about 70
second per assembly. Bot of the assembly speeds of "Grip Housing Assembly" and the
"Final Assembly" are about 70 seconds. To balance the assembly speed, the "Testing"
and "Packaging" stations are combined to reach assembly speed of 70 seconds. Because
the speed of assembling grip housing is three times the speed of assembling transmission
module, three "Transmission Assembly" stations are employed to balance the total
assembly speed.
The final assembly testing is done at the end of the assembly considering that the
sub-module testing impractical. That is, the transmission assembly and the grip housing
assembly cannot be tested separately. If the assembly is failed upon the testing, the
product is sent to the repair station. The repair station is going to "retest", "disassemble",
and "reassemble" the product. The repair results are sent back to the "Buffer 5" to be
packaged. It is assumed that 1 out of 100 final assembly will have to be repaired.
The statistics and capabilities of each station in the assembly process are
summarized in the following table. The capacity of the buffers were set according to the
required size from some simulation runs (see the histograms below).
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 68 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
Out
2.875 Mechanical Assembly and Its Role in Product Development
Process (seconds)
Constant rate =
80/s
Constant rate =
80/s
Normal ( = 218, 
= 21.8)
Failure (seconds)1
-
Repair (seconds)2
-
-
-
Normal ( = 7200,
 = 900)
Log-Normal ( =
900,  = 200)
Normal ( = 218, 
= 21.8)
Normal ( = 7200,
 = 900)
Log-Normal ( =
900,  = 200)
Normal ( = 218, 
= 21.8)
Normal ( = 7200,
 = 900)
Log-Normal ( =
900,  = 200)
Normal ( = 69.7,
 = 7)
Normal ( = 7200,
 = 900)
Log-Normal ( =
900,  = 200)
Normal ( = 72.7,
 = 7.3)
Normal ( = 68.7,
 = 6.9)
Normal ( = 7200,
 = 900)
Normal ( = 7200,
 = 900)
Log-Normal ( =
900,  = 200)
Log-Normal ( =
900,  = 200)
Normal ( = 7200,
 = 900)
Log-Normal ( =
900,  = 200)
Buffer 1 (Buff_3)
Normal ( = 1200,
 = 300)
Capacity = 24
4
Buffer 2 (Buff_4)
Capacity = 30
9
Buffer 3 (Buff_9)
Capacity = 24
10
Buffer 4 (Buff_10)
Capacity = 30
12
Buffer 5 (Buff_12)
Capacity = 30
14
1
Buffer 6 (Buff_14)
Out (Inou_1)
Capacity = 5
-
No.
1
Name
In 1 (Inou_1)
2
In 2 (Inou_2)
5
15
Transmission
Assembly
1
(Mach_5)
Transmission
Assembly
2
(Mach_6)
Transmission
Assembly
3
(Mach_7)
Grip
Housing
Assembly
(Mach_8)
Final
Assembly
(Mach_11)
Testing &
Packaging
(Mach_13)
Repair (Mach_15)
3
6
7
8
11
13
-
-
Remark
Transmission
components
Grip
Housing
components
Transmission
component buffer
Grip
housing
component buffer
Finished
transmission
assembly buffer
Finished
grip
housing assembly
buffer
Finished
screwdriver
assembly buffer
Repair buffer
Packaged
screwdrivers
Because the limitation of the student version of Taylor II software to allow only up to 15
elements, the "Out" element after the successful "Testing and Packaging" is combined
with the "Inp 1." The Taylor II layout model is shown in the following figure.
1
For all these manual operations, failure is the scheduled (allowed) break at about every 2 hours.
Repair means the length of allowable break for about 15 minutes. Log-normal distribution is assumed
because people tend to take a longer than a shorter break than allowed.
2
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 69 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
An example of simulation run result is shown below.
screwd4
Taylor II Element report
Date: 27-11-1999 Time:
22:30
========================================================================
=====
Cluster Elnr
Elname Produced AvgQueue
Util
Down
-------- ---- -------- -------- -------- ------ -----0
1 Inou_1
360
1.00 100.00
0
2 Inou_2
360
1.00 100.00
0
3 Buff_3
349
5.54
0
4 Buff_4
356
4.13
0
5 Mach_5
116
0.99 89.59
9.13
0
6 Mach_6
117
0.97 89.29
8.21
0
7 Mach_7
113
0.97 85.46 11.27
0
8 Mach_8
355
0.96 86.73
9.40
0
9 Buff_9
334
9.41
0
10 Buff_10
12.78
0
11 Mach_11
333
0.94 83.88 10.08
0
12 Buff_12
332
3.31
0
13 Mach_13
331
0.90 79.06 11.31
0
14 Buff_14
6
0.05
0
15 Mach_15
5
0.26 23.42
9.61
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 70 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
The queue utilization in each buffer is shown in the following histograms.
No. 3 - Buffer 1
No. 4 – Buffer 2
No. 9 – Buffer 3
No. 10 – Buffer 4
No. 12 – Buffer 5
No. 14 – Buffer 6
At the beginning of operation when there is nobody taking a break, the buffers are almost
empty. The condition of high number of items in the buffers happened when the assembly
operators start taking breaks. The large size of buffers are the main concern for the
efficiency because in addition to taking space, buffers also mean a tight up capital
because the work-in-process inventory is sitting idle in the factory. The length of time
that a work in process inventory is sitting in a buffer is shown in the following waiting
time histograms.
No. 3 - Buffer 1
No. 4 – Buffer 2
No. 9 – Buffer 3
No. 10 – Buffer 4
No. 12 – Buffer 5
No. 14 – Buffer 6
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 71 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Therefore, it is preferable to minimize the amount of inventory and keeping the
throughput as high as possible. This can be done by some alternatives as follows:
 To use the underutilized "Repair" person to do various tasks to substitute a person
that is taking a break. This simulation model of this situation is too complicated for
the student version to handle. Another alternative is described next.
 Schedule the break at the same time. Therefore, during the break, the whole assembly
line is shut down so that nobody is accumulating work in progress inventory for the
next station. The duration of breaks are kept the same as the previous simulation
setting. That is, they are following Log-Normal distribution with mean of 15 minutes
and standard deviation of 200 seconds.
screwd5
Taylor II Element report
Date: 28-11-1999 Time:
12:34
========================================================================
=====
Cluster Elnr
Elname Produced AvgQueue
Util
Down
-------- ---- -------- -------- -------- ------ -----0
1 Inou_1
360
1.00 100.00
0
2 Inou_2
360
1.00 100.00
0
3 Buff_3
350
5.83
0
4 Buff_4
355
5.45
0
5 Mach_5
115
0.98 87.65
9.86
0
6 Mach_6
118
0.97 88.34
8.30
0
7 Mach_7
114
0.98 87.72
9.87
0
8 Mach_8
354
0.97 86.32 10.43
0
9 Buff_9
346
1.97
0
10 Buff_10
4.31
0
11 Mach_11
345
0.97 88.15
8.90
0
12 Buff_12
347
1.04
0
13 Mach_13
346
0.93 83.03 10.41
0
14 Buff_14
6
0
15 Mach_15
6
0.24 23.61 11.14
The queue size of each buffer is shown in the following histogram.
No. 3 - Buffer 1
No. 4 – Buffer 2
No. 9 – Buffer 3
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 72 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
No. 10 – Buffer 4
No. 12 – Buffer 5
No. 14 – Buffer 6
The corresponding waiting time in queue is shown in the following histogram.
No. 3 - Buffer 1
No. 4 – Buffer 2
No. 9 – Buffer 3
No. 10 – Buffer 4
No. 12 – Buffer 5
No. 14 – Buffer 6
Notice now that the required size of buffers 3, 4, 5, and 6 become much smaller than
before. The size of buffers 1 and 2 are still the same because we assume that a constant
stream of components are coming to these two buffers.
A more realistic situation can be simulated by assuming that the stream of
components from "In 1" and "In 2" also follow random pattern with "breaks" represented
by MTBF and MTTR. Negative exponential distributions are used for both the inputs to
represent a constant supply with random fluctuation. The following are the results of the
simulation with simulation parameters shown in the following table.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 73 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Process (seconds)
Neg. exponential, 
= 80/s
Neg. exponential, 
= 80/s
Normal ( = 218, 
= 21.8)
Failure (seconds)3
Constant
every
7200 s
Constant
every
7200 s
Constant
every
7200 s
Repair (seconds)4
Log-Normal ( =
900,  = 200)
Log-Normal ( =
900,  = 200)
Log-Normal ( =
900,  = 200)
Normal ( = 218, 
= 21.8)
Constant
7200 s
every
Log-Normal ( =
900,  = 200)
Normal ( = 218, 
= 21.8)
Constant
7200 s
every
Log-Normal ( =
900,  = 200)
Normal ( = 69.7,
 = 7)
Constant
7200 s
every
Log-Normal ( =
900,  = 200)
Normal ( = 72.7,
 = 7.3)
Normal ( = 68.7,
 = 6.9)
Constant
7200 s
Constant
7200 s
every
Log-Normal ( =
900,  = 200)
Log-Normal ( =
900,  = 200)
Constant
7200 s
every
Buffer 1 (Buff_3)
Normal ( = 1200,
 = 300)
Capacity = 20
4
Buffer 2 (Buff_4)
Capacity = 15
9
Buffer 3 (Buff_9)
Capacity = 25
10
Buffer 4 (Buff_10)
Capacity = 10
12
Buffer 5 (Buff_12)
Capacity = 15
14
1
Buffer 6 (Buff_14)
Out (Inou_1)
Capacity = 3
-
No.
1
Name
In 1 (Inou_1)
2
In 2 (Inou_2)
5
15
Transmission
Assembly
1
(Mach_5)
Transmission
Assembly
2
(Mach_6)
Transmission
Assembly
3
(Mach_7)
Grip
Housing
Assembly
(Mach_8)
Final
Assembly
(Mach_11)
Testing &
Packaging
(Mach_13)
Repair (Mach_15)
3
6
7
8
11
13
-
every
Remark
Transmission
components
Grip
Housing
components
Log-Normal ( =
900,  = 200)
-
Transmission
component buffer
Grip
housing
component buffer
Finished
transmission
assembly buffer
Finished
grip
housing assembly
buffer
Finished
screwdriver
assembly buffer
Repair buffer
Packaged
screwdrivers
screwd6
Taylor II Element report
Date: 28-11-1999 Time: 12:55
========================================================================
Cluster Elnr
Elname Produced AvgQueue
Util
Down
-------- ---- -------- -------- -------- ------ -----0
1 Inou_1
317
1.00 92.64
7.36
0
2 Inou_2
304
1.00 90.34
9.66
0
3 Buff_3
317
2.65
0
4 Buff_4
304
1.95
0
5 Mach_5
110
0.92 84.24
8.09
3
For all these manual operations, failure is the scheduled (allowed) break at every 2 hours.
Repair means the length of allowable break for about 15 minutes. Log-normal distribution is assumed
because people tend to take a longer than a shorter break than allowed.
4
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 74 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
0
0
0
0
0
0
0
0
0
0
6
7
8
9
10
11
12
13
14
15
Mach_6
Mach_7
Mach_8
Buff_9
Buff_10
Mach_11
Buff_12
Mach_13
Buff_14
Mach_15
105
99
304
304
304
309
308
5
5
0.84
0.79
0.83
7.46
1.05
0.85
1.21
0.82
0.03
0.27
78.18
74.12
73.06
9.14
9.14
9.81
76.92
8.03
73.25
10.38
23.04
11.40
The corresponding Queue size and waiting time histogram are shown in the following
figure.
Queue size hitogram
No. 3 - Buffer 1
No. 4 – Buffer 2
No. 9 – Buffer 3
No. 10 – Buffer 4
No. 12 – Buffer 5
No. 14 – Buffer 6
No. 4 – Buffer 2
No. 9 – Buffer 3
Waiting time histogram
No. 3 - Buffer 1
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 75 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
No. 10 – Buffer 4
No. 12 – Buffer 5
No. 14 – Buffer 6
6.2.2 Selection of Final Assembly Process
To make more realistic condition, the "Input" elements "In 1" and "In 2" are
assumed to supply buffers 1 and 2 in batch sizes of 20 according to an exponential
distribution with rate of 900 seconds (15 minutes). This is the estimated time to move the
components to the buffers of "Transmission Assembly" and "Grip Housing Assembly"
stations. Using this assumption, an investigation was conducted to determine the proper
size of the rest of the buffers. The important buffers will be the buffers before the
bottleneck station: "Final Assembly" with the longest cycle time (72.7 seconds). The
results of the investigation are summarized in the following table.
No. Station
1 In 1 (Inou_1)
2 In 2 (Inou_2)
3 Buffer 1 (Buff_3)
4 Buffer 2 (Buff_4)
5 Transmission
Assembly 1 (Mach_5)
6 Transmission
Assembly 2 (Mach_6)
7 Transmission
Assembly 3 (Mach_7)
8 Grip Housing
Assembly (Mach_8)
9 Buffer 3 (Buff_9)
10 Buffer 4 (Buff_10)
11 Final Assembly
(Mach_11)
12 Buffer 5 (Buff_12)
13 Testing & Packaging
(Mach_13)
14 Buffer 6 (Buff_14)
15 Repair (Mach_15)
Finish Output
Buffer size = Buffer size = Buffer size = Buffer size =
1
5
10
20
53.7
66.25
53.33
48.88
29.24
31.71
29.57
32.09
59.9
73.98
76.62
77.24
61.72
70.22
77.94
77.16
62.14
71.77
75.54
77.75
58.25
69.74
75.12
74.83
60.7
71.63
74.94
73.67
57.88
69.98
72.85
70.82
21.92
244
44.68
295
20
304
21.55
294
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 76 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Buffer size = 10 for the bottleneck station is selected because it is not as much different
from buffer size = 5 in terms of size requirement, but it provides higher utilization as well
as higher throughput. Buffer #5 and #6 are set equal to 1 (no buffer) because these are not
bottleneck stations. The queue and waiting time histograms for this selected setting are
shown below.
Queue Histograms
No. 3 – Buffer 1
No. 4 – Buffer 2
No.9 – Buffer 3
No. 10 – Buffer 4
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 77 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
Waiting Time Histograms
No. 3 – Buffer 1
No. 4 – Buffer 2
No.9 – Buffer 3
No. 10 – Buffer 4
The statistics of this assembly operation is as follow.
screwd7
Taylor II Element report
Date: 29-11-1999 Time: 19:55
========================================================================
Cluster Elnr
Elname Produced AvgQueue
Util
Down
-------- ---- -------- -------- -------- ------ -----0
1 Inou_1
320
1.00 53.33 10.02
0
2 Inou_2
320
1.00 29.57
9.82
0
3 Buff_3
307
8.77
0
4 Buff_4
313
10.84
0
5 Mach_5
102
0.86 76.62
9.11
0
6 Mach_6
102
0.84 77.94
6.48
0
7 Mach_7
100
0.85 75.54
9.37
0
8 Mach_8
312
0.98 75.12
9.06
0
9 Buff_9
302
1.55
0
10 Buff_10
9.37
0
11 Mach_11
301
0.85 74.94
9.33
0
12 Buff_12
305
0.21
0
13 Mach_13
304
0.82 72.85
9.01
0
14 Buff_14
5
0.08
0
15 Mach_15
4
0.28 20.00 10.17
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 78 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999
2.875 Mechanical Assembly and Its Role in Product Development
In general, the utilization of the stations (around 75%) are considered appropriate for the
assembly workers. The Input stations (Inou_1 and Inou_2) and the repair station
(Mach_15) total utilization is about 100% (53.33% + 29.57% + 20%). These three tasks
are performed by 2 people instead of 3 people. That is, Inou_2 and repair are done by the
same person. A low utilization value of 50% is considered appropriate for these tasks as
these people need to walk around in between jobs to transfer the raw materials.
_________________________________________________________________________________________________________
Originators: Sudjianto/Clark/Oak/Shukla/Tanabe
Page 79 of 79
Date Initiated: September 29, 1999
fInal_report.doc
Date Revised: December 5, 1999